I agree with this. For the last ~4 years I have been working to turn my Minecraft server into a free browser game on a custom engine.

Though in Roblox's case, there's two additional factors helping the success of games on its platform besides being free to play

- Roblox has become the de-facto portal from which lots of people play games by default, especially on mobile devices like tablets where discovery for other games (that aren't P2W and can spam ads) is very poor

- Multiplayer games are exceptionally easy to develop on Roblox. (With a standalone game you have to grind on an engine for years like what I'm doing. I'm developing thousands of LOC per weekend with a multi-agent setup and there is just so much necessary complexity that launching an alpha build will take months.)