I think what you're missing is an explanation on why there should be any correlation between being a good developer/employee with writing a blog. Sure, you can say communication skills, but you want to test for that anyway.
I actually think that we'd have a much better job market without any of this.
I'm also among the people that see too much pointless content being published simply for hidden advertising, including by companies.
I don't think there's a correlation between writing a blog and being a good developer.
I think there's a small correlation between "having a tiny bit of evidence online that you're capable of solving problems" and "getting invited to an in-person interview" - at least given my own experience at the companies that I've worked at (and hired for).
That said, I do think there's a strong correlation between being good at written communication and being a great senior / staff-level engineer.
I actually think that we'd have a much better job market without any of this.
I'm also among the people that see too much pointless content being published simply for hidden advertising, including by companies.