Fair question (I'm neither the blog author or the person who linked it here).
I read the short blog entry and the why is not answered.
My own reasons for de-Googling is that I'm uncomfortable with how I pay for Google's services (with my usage data, time, attention, media data, etc). I still have a gmail account because I'm skeptical it won't be reused in a potentially-harmful-to-me-or-others way and because I haven't put in the time to answer that concern and go through the account-deletion steps. I have it automatically send any emails (very few these days) to my ProtonMail account, which I pay for. I'd rather pay a few US dollars a month to a company that at least doesn't seem based on selling more-more-more (Google being an advertisement company).