Well, as the article says, Git already fixed the issue, SHA-256 is already supported. Now it's up to GitHub, GitLab and the innumerable other platform/tool providers to update their solutions, until then Git can't in good conscience make SHA-256 the default, because that would condemn a repository to a life in eternal isolation...
Per the article, the biggest problem isn't third party integration but that there is no interop with old repos. The feature is in an experimental state right now (and labeled as such), so you can't and shouldn't expect GitHub/GitLab/anyone to start using it in production
