Because they're self-aware perfectionists and are actively working to stop it, because they reach for all kinds of tools like grammar checkers and AI, but they're aware that using those will make the post lose "their" voice, or the human element of the post.
And that's, I think, a valid choice; you can choose to use all the tools and make something gramatically and stylistically as close to perfect, but who would want to read something as dry? That's for formal writing, and blog posts are not formal.
If you use grammar checker as a grammar checker, it wont make you loose your voice. It will make you use correct grammar.
> you can choose to use all the tools and make something gramatically and stylistically as close to perfect, but who would want to read something as dry
If it is dry, then it is not stylistically perfect. Per definition, dry writing is just an imperfect writing. Stylistically perfect writing does not have to be dry and usually is not dry.
What happens here is that people use "stylistically perfect" when they mean "followed a bad stylistic advice".
Reading what you write for editing does not make a text lose your voice. If anything, it amplifies it, you get to ensure that what you intended to say was said.
Not reading what you write smells more like laziness.
Same thing for spell checks, grammar checks, and even AI usage. If you use things lazily, the result will be lazy as well.
Instead of asking for an AI tool to write your thoughts in your place, you can write it yourself and ask it to criticize your text, instruct it to not rewrite anything, only give you an overall picture of text clarity, sentiment, etc.
But that of course would require more work. Asking ChatGPT to produce a text based on a lazily written, bullet point list of brainfarts is probably easier.