The fact that we can notice this even in the startup sector speaks even louder.
I work at a large agency, we have to explain our design rationale every day to people that have zero design backgrounds. The better we do this, the better we're able to do our job. If we acted like assholes we wouldn't be in business very long.
Exactly, the really good and professional designers I worked with spent a lot of time to explain and work with me and show evidence for their approach.
To be condescending and dismissive is a warning sign that maybe somebody is being arbitrary and has to cover up their lack of professional development.
On the other side there is also a benefit of giving technical input about a design, sometimes there are more robust solutions from a technical standpoint that gel with what the designer does.
I think both design and implementation are more efficient this way. It's also more fun.
Honestly most ux designers I've worked with were graphic designers by training and previous experience.
I think to the same extent the phenomenon you describe exists, experts (perhaps even engineers) loathe accepting and abiding expertise outside their domain that impacts or determines their work.
It’s human nature to want agency. Achieving some measure of mastery can confuse one into a growing sense of entitlement to agency…and this sentiments like yours.