I think game ideas can get copied everywhere but it happens much faster on Roblox and there is almost no recourse for the smaller developer who got copied.

The platform doesn't care when someone makes a copy, there's no way for players to push back and actually hurt the developer making the copy (unlike Steam where trying to do it will get you bombarded with negative reviews and buried by the algorithm), and superficial visual quality and marketing attracts players more than actual gameplay quality.