Board Thread:Roblox help and discussion/@comment-35433437-20190808194924/@comment-35998649-20190808195056

Roblox believed it was an outdated feature and thus removed it.

Personally, I think it was abused by exploiters who used guests to get away with exploiting (as far as I know, that can be harder to monitor). It probably just not encouraged users to make accounts, which Roblox wants people to do.