TL;DR summary: WB had a contract with Sony, both of which have expensive legal teams and knew exactly what they were getting themselves into, so Sony knowingly chose the cheaper option (a shorter lock-in of the right to make that content available). Sony had contracts (implied and possibly with an agreement, part or all of which might not even be valid in various legal jurisdictions due to Consumer Protection Legislation) between legally-well-armed Sony and zero-legal-knowledge retail customers which, at minimum was portrayed by Sony in so unclear terms (at worse, purposefully to deceive) that said zero-legal-knowledge retail customers thought they were buying something when contractually it was a rental. How exactly would WB - who negotiated with a legal expert counterparty who knew exactly what they were doing - to blame rather than Sony - who took advantage of the legal naivity of retail customers and quite possibly is leveraging the high costs of legal action against them so as not to have to refund said customers? The legally expert and very well funded counterparty - Sony - taking advantage of a non-expert and much less well funded counterparty - retail customers - seems a vastly most likely place for shennennigans than the one between two well funded companies with their own legal experts, Sony and WB.

Sony chose to sign a contract with WB where it did not lock-in WB to certain responsabilities for a large time period - say 20 years - and instead chose a shorter time period (which both Business 101 and Asset Pricing Theory indicate as a cheaper option - locking-in certain rights contractually tends to cost more the longer the lock-in period) and per what you say, covered its liability on the client side with clausules in the user licence agreement that essentially meant they could take away any content their customer purchased.

Even putting aside the legality of those clauses and of the EULA itself (if* it was presented to the client after the client paid, it's legally deemed is void and null per the legislation in most of the World because it's considered an attempt at changing the terms of a contract after it has been closed), I don't see which WB is to blame for Sony having chosen a contract length in their agreement with WB that did not guarantee that Sony's own clients would not be removed access to the digital media they had been led to believe they bought.

It seems to me that WB had a contractual arrangement with Sony (NOT with Sony's client's) with which Sony agreeded (and, having lots of expensive lawyers, it can hardly be claimed that Sony did not fully understood the implications of that contract) and they fullfilled their end of the contract, whilsy Sony on the other hand had a contractual relation with retail customers (which are not expected to be anywhere as good in understanding the ins and outs of that contract as Sony's Lawyers) and which led many if not most of the retail clients to believe they had purchased something which was not in fact sold and if the EULA was only presented to said retail clients after they paid, it wasn't even backed by a valid contract.

It seems to me that it was Sony that deceived their clients and (if having done so purposefully, it might amount to Fraud, something a Court Of Law would have to rule on), possibly using clauses which are invalid when used with retail clients or not making it sufficiently clear to said retail clients that the nature of the transaction was not a sale but a rental for an indetermined period (both of these depending very much on the legislation of country that retail client is based) and possibly using means that are not even a valid contract in most jurisdiction (i.e. an EULA which is presented post-payment).

In summary, the WB-Sony contract was between two sets of legal experts of big companies, hence both knew perfectly well what they were getting themselves into, whilst the Sony-Retail_Customer contract was between one set of legal experts and individuals most of which with no legal expertise at all and no access to cheap enough legal expertise to analyse all such contract, and which further, had clauses going against several consumer protection laws in several countrues and possibly (if they did it by that order, which I don't really know) using an EULA presented to the customer after the sale, something which is null and void in contract terms in most of the World because it's an unilateral attempt at forcing a change in contract terms after the implied contract of the sale has been closed.

How exactly does it make sense to conclude that its WB - the guys that entered into a clear contract with a legally well advised counterparty - who are to blame, rather than Sony who seem to at the very least misportrayed the nature of the sale they were making to retail costumers (who are not legal experts) possibly using means which aren't even valid under contract law or due to customer protections?

I mean, I can see how you can claim that Sony's actions were within their contractual terms with the Retail Customers (especially in the Fuck-You-Pleb US with its nearly non-existent consumer protections) so maybe it is all legal, but blaming WB who had a contractual relationship with Sony, who most definitelly have the lawyers to make sure that contract was exactly as they wanted to is ridiculous - Sony absolutelly had the power to pay more and get a contract with WB which, say, would guaranteed that media sold to consumers by Sony would remain available forever and only new sales would stop at the end of a certain period if WB did not renew the contract, they just chose not to pay more and rely on the expectation that they could screw their own retail customers who would be de facto unable to be compensated because of the cost of pursuing a legal case against Sony to get that compensated.