Blurring the background is different than putting some other sort of background there. That doesn't bother me nearly as much.

Regardless, I am someone who never pays for a haircut and has very casual clothes. But this is something that, to me, indicates a complete lack of sensitivity to aesthetics, and in a large number of jobs/roles, that's a really bad sign.

There's also a bit of the "what is so important to hide?" question.

It's great if you can ignore such things, but not everyone can or does. This is almost like someone who has poor hygiene, who has dirty hair or a bit of a smell to them. Anyone would advise such a person to put in a bit of effort if they want career success. Same thing.