I think a lot of this comes from a strong sense of entitlement. We're told "the customer is always right", so when a genuine accident or situation arises where they have to downgrade something, either because they run out of time or because they can't get it to perform well on the console version in the end, we see it in the poorest faith, as if they are trying to lie to us, and we feel justified as if we have some kind of obligation and right to lose our minds over it. Most devs just want to make the best game they can. No one wants their name attached to a project that is known for being disappointing or not living up to what was promised. I assure you that any creative person in the industry sees that as a nightmare scenario.
There are very few times where I think it's justified to be upset. Cyberpunk is probably the biggest one in recent memory, in part because the information suggests that the game just needed more time in the oven (one year seemed to do it with the recent upgrade, but I personally would have preferred two or three to get some more of the removed content back in there). I don't think that there was ever a direct intention to lie until it became apparent that cuts were going to have to be made in the last year or so of development. At that point, yes, it becomes something worth being upset over, because they never communicated this, but prior to that, all of the promises and things they spoke of seemed like things they genuinely intended for the final product to have, and you can see this even in the game, as there are many areas where you can see content having been somewhat roughly and obviously cut out. I find it hard to call that "lying". The deception there is more in the way the marketing carried on as if this hadn't happened (I think the worst example is the use of a literal montage scene in the advertising, which made it seem like it was a bunch of in-game experiences... nope, it's literally a montage, OWNED). That's more worth being upset about than the cuts and downgrades themselves.
Typically, I just take trailers with a grain of salt at the moment. Sometimes I don't even watch them if the game is something I know I'm already going to be interested in. Unless I'm watching footage that is considered final gameplay, anything and everything is subject to change heavily even a week before release. AAA game development in particular involves a ton of moving parts, so it's not surprising that we have to rely upon some scripted footage as things come together.
Why make myself upset about what something could have been instead of just appreciating it for what it is? Life's too short to work ourselves up over feeling entitled in this way. If something doesn't seem right to you, don't buy the game, sure, but getting worked up over it? Nah.