I am actually working on doing the opposite and getting rid of my custom domains. I’m not really doing anything with them except spending money to have them. Working on getting all my socials to basically match with a similar username and just go from there.
If I host my blog, assuming I actually start making posts, on GitHub with a custom domain, when I die then the domain will likely expire and the blog is no longer accessible. If I keep it with my GitHub .io url, it’ll be there for as long as the account is there.