It's interesting that you used "wants" in the first sentence and "needs" in the second.

Not saying that you're totally wrong, but I think this difference is not necessarily a deliberate decision by individual engineers, or caused by personality or skill level.

The employee market demographics surely play a role, but this is about concretions, not generalizations.

There is no lack of (often poor) generalizations when it comes to the skills and requirements demanded by BE and FE roles, respectively.

Not wanting to dismiss your idea / the grain of truth. But IMO you are falsely generalizing.

Also, there are not only FE devs claiming to be "full stack" when they don't know HTTP basics.

There are also BE developers with similarly daunting knowledge gaps.

Or in other words, in both worlds there are juniors masquerading as seniors and the other way around, depending on the organization.