It's the same network effect with other megacorp, we could argue the same about X/Instagram/Mastodon, the question could be changed to: Do you want your children to be groomed to use closed source ecosystem from shady companies or do you prefer they gain experience in using relatively open ecosystem ?
Luanti let you make multiplayer games/mods too. For Minecraft there way to play outside of Microsoft sanctioned versions and servers.
Nobody uses platforms because they are are looking to exercise billions of options. The point is easy commonality. You sit next to a kid, and, what do you know, they are into Roblox too. Cool. Wanna play?
For Minecraft random people are more of a nuisance than an asset, but for a Roblox obby there is an expectation that other people will check it out.