It's not the interface, it's the web hosting. People want a free destination server that's up 24/7 to store their repository.
If it was only the web interface, people could locally install GitLab or Gitea to get a web browser UI. (Or use whatever modern IDE code editor to have a GUI instead of a CLI for git commands.) But doing that still doesn't solve what GitHub solves: a public server to host the files, issue tracking, etc.
Before git & Github, people put source code for public access on SourceForge and CodeProject. The reason was the same: a zero-cost way to share code with everybody.
A 24/7 repository and a 24/7 web URL for the code. Those two features together let devs inspect and download code, and open and discuss issues.
The URL also let automated tools download and install packages.
Familiar UI, network effects made the rest.
I'm really looking forward to federated forges.