Since GitHub Pages lets you attach a custom domain, it seems like the perfect choice.
I would expect their CDN to be pretty awesome. And updating the website with a simple git push seems convenient.
If you're curious, Netlify is one popular alternative that is easy to get in to even without much experience. I would say even at the free tiers Netlify is easily a cut above Github for static hosting, and it hooks into github near perfect straight out of the box if that is something you value.
Because some people may not want to depend even more on Big Tech (i.e. Microsoft) than they already do
One reason would be if your site violates the TOS or acceptable use policy. GitHub bans "excessive bandwidth" without defining what that is for example. For a small blog about technology you are probably fine.
For static websites, CDNs are largely unnecessary. My potato of a website hosted from a computer in my living room has been on the front page of HN several times without as much as increasing its fan speed.
It took Elon Musk tweeting a link to one of my blog posts before it started struggling to serve pages. I think it ran out of file descriptors, but I've increased that limit now.
I don't like github pages because it's quite slow to deploy. Sometimes it takes more than a couple of minutes just to update a small file after the git push.
$ curl https://nobodywasishere.github.io # moved to https://blog.eowyn.net
<html>
<head><title>301 Moved Permanently</title></head>
<body>
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx</center>
</body>
</html>
$ curl https://blog.eowyn.net/vhdlref-jtd # moved to https://blog.eowyn.net/vhdlref
<html>
<head><title>301 Moved Permanently</title></head>
<body>
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx</center>
</body>
</html> ~ % curl -i 'https://kotokaze.github.io/'
HTTP/2 301
server: GitHub.com
content-type: text/html
permissions-policy: interest-cohort=()
location: http://github.kotokaze.net/A 301 (or 302) redirect means setting the status code header to 301 and providing a location header with the place to redirect to. Last I checked GitHub doesn't allow any of this, or setting any other headers (like cache-control). To work around this, I've been putting cloudflare in front of my site which lets me use page rules to set redirects if necessary.