Gitlab/Bitbucket are not "dumps" for projects you deem useless, and "useless" projects are not useless at all from an educational point of view. Gitlab and Bitbucket are exactly the same as Github and should have both "serious" and "useless" projects the same.
Using a personal Gitlab instance or anything similar for that is a terrible idea because it costs substantial time and money of individual developers and severely hurts discoverability.
People should put their "useless" projects wherever they want and are permitted to.