Those people (software engineers) aren’t making the decisions around the product in larger companies. These are done by Product Managers and UX Specialists/Designers.

They (mostly) don't make the bigger decisions, bigger design choices, true

But for minor stuff/fixes it's easy to slip something that's awkward or not very usable.

Or a legacy interface is still being used (because the developer thought it out - since the company was smaller, or a specific screen was overlooked) and that's not a great interface

That may be the case in companies without proper responsibility distinction but in those with (usually the bigger ones), not even small decisions are made solely by software engineers. They are always double checked by the Product Management because any requested change has to come from the Product Management and has to be signed-off by them. In a company like Zoom everything you are seeing in the UI isn’t the result of something that slipped through solely by the engineer but was reviewed and thought out by multiple people who don’t touch the code.

So I can be mad at more than one person, when Google Drive's or iOS' user interface is misbehaving

Someone failed a whiteboard interview?