Lots of stuff involved. For one, globalization and mechanization are driving forces. The Wikipedia page for pretty much the official term enshittification has a link to another page describing another term "rent-seeking behavior" that means:

Rent-seeking is the act of growing one's existing wealth by manipulating the social or political environment without creating new wealth.[1] Rent-seeking activities have negative effects on the rest of society.

i.e. when something just takes takes takes and never gives, that describes the broken state.

Also in the late 70s, corporations were given enormous power and now they have more power than any individual human beings - even their CEOs exist as slaves to their whims, except to the extent that they also are shareholders in their stocks. Humans have to do things like breathe, eat, die, and pay their debts, but corporations have special legal exemptions and don't have to do any of this. And this even without the extra special stuff done on top of the normal when they are deemed too big to fail - e.g. banks can smuggle money from genocidal terrorists and get away with it, but don't try that at home unless you too are a corporation of at least a certain size, and can afford to bribe/threaten the life of your own personal judge!

And underlying it all is the dirty word politics, an ancient Greek word meaning "how (the process by which) we all agree", or another definition is "who gets what, when, how". Every time something happens, whether it be genocide or school shootings or even just allowing corporations to claim one thing on the internet while delivering the exact opposite of that (without consequences), it is this "politics" that decides the outcome - like WILL we support Ukraine (financially and/or otherwise) to defend itself from Russian aggression or WON'T we? And on that note, there is a fascinating series of videos on YouTube called "The Alt-Right Playbook", which explains why conservatives like what has happened the last 10 years - e.g. not paying taxes is "smart" and Musk taking over Twitter is "his own business/matter", and corporations having all the stuff while we merely working stiffs have none of it is very much not a byproduct but the literal point of the systems, which is very much working as designed. You may call it words like "inflation" and "price gouging", but companies charge what the market can bear, so according to that philosophy, whatever you call it is a good thing, very much not something that government should be doing anything to stop, and in fact perhaps corporations should be given even more power on top of that.

Like everything else - e.g. physics, biology, chemistry, economics, etc. - you are not going to understand everything in less than let's say a year, or possibly a decade, but you will get there if you really want to know. The short answer imho is that giant corporations now have more rights than mere human beings and thus normal folks are fast becoming obsolete. We will either be killed off (a large number anyway) and the rest absorbed into becoming slaves for them, the same as has happened many times throughout history. And we will be shocked, shocked I tell you, shocked, as if this entirely predictable outcome had never happened before and never would again. Basically they are putting in huge efforts to do these things, and very few people are bothering to lift a finger to try and stop it so... how is it not inevitable? About the only thing I see working against corporate enshittification is FOSS and piracy, each providing for free what corporations want you to pay for.