I want a big, swapable battery that uses 18650 cells,

I mean, me too. I think that having less than a 100 Wh battery is nuts, but it's essentially impossible to find them.

I think that a couple of things have killed this:

• Cost. Cutting battery size is an easy way to cut cost, and it's less-explicit than, say, cutting RAM, as vendors often list a non-standardized "hours of battery life".

• USB PD plus external power stations. I think the expectation is that one will get one and having the user just use external ports makes life easier for the vendor and means that they don't need to deal with counterfeit batteries and such. Also moves heat out of the laptop. I would be more sympathetic to this if there were a standard for a laptop to start automatically drawing from an external USB powerstation when its internal battery gets low, rather than requiring manually-triggering charging.

• Weight. Apparently some people are super-rabid about laptop weight.