Because it sold "legitimacy" of your blog as a subdomain.
Being a legit tech blogger is not about the domain, it is about having a significant repository of articles over many years, and for the majority of those articles to be at least insightful or entertaining, if not educational or maybe even introduce something completely novel.
You can't achieve that by signing up at a website which instantly nags its users to sign up to your mailing list. Substack sucks for the same reason.
If you want to be a legit tech blogger, get writing, and write well. See how you're going in a few years.
Being a legit tech blogger is not about the domain, it is about having a significant repository of articles over many years, and for the majority of those articles to be at least insightful or entertaining, if not educational or maybe even introduce something completely novel.
You can't achieve that by signing up at a website which instantly nags its users to sign up to your mailing list. Substack sucks for the same reason.
If you want to be a legit tech blogger, get writing, and write well. See how you're going in a few years.