The most common cause of this is propaganda. It's like the old joke "Taking tech advice from the pages of Forbes is like taking financial advice from Popular Mechanics"

A great many "executives" are making these decisions whilst unqualified to do, based entirely on what they've read online and in magazines with little to no technical prowess. Then they go looking for someone to do it the "hot and trendy" way, not caring a whit if the "framework stupid" is right, proper, or in any way necessary.

Propaganda -- which I constantly point out -- plays a large role in that. Bandwagon -- everyone is doing it, you should too. Card stacking via bad examples that make the garbage look good by comparison. Authority fallacy / transfer in the form of saying stuff like "But it was made at Twitter"

All whilst providing not one legitimate example of why the CLAIMS of it being "better" are in any way factual.

And the more you start to understand HTML and CSS, the bigger a steaming dung-heap of lies the "framework stupid" vomits up

It's a sad truth, people hiring others to do a job, usually are doing so because they're not qualified to do the job themselves! And that leads to the continual annoyance that they still insist on choosing what stack is used despite their lack of the most basic knowledge of the job.