Alright, a little touchy topic here. The comparison between Minecraft and Roblox was almost like how many people compared Team Fortress 2 and Overwatch, people say one or the other copied each other, flame wars and lawsuits were almost made.
Minecraft at it's core is a survival game where players must learn to adapt to certain environments to be able to survive. Mods that add technology, magic and whatnot allow the game to literally become any genre. You could make a horror map, a minigame like Capture the Flag or Team Deathmatch. You could literally recreate certain games like Amnesia or Slender in Minecraft.
Roblox is a platform for games, not a game in it of itself, people can create their own games in Roblox Studio for the enjoyment of others. Roblox also has an economy, built from the platform's currency Robux, where people could buy gamepasses in games to gain access to more features. Customize their Avatars with hats and cosmetics. And compete with other people in Company Sponsored Events for virtual prizes.
Roblox heavily relies on the multiplayer aspect of gaming, while Minecraft allows both singleplayer and multiplayer features. In a way, Minecraft paved the way for multi-genre games to exist. The Communities of both parties also host a majority of younger audiences ranging from 9-12. Young Adults and Teenagers could profit from either of them to support them in College and sometimes get hired by them to work full-time.
I love Minecraft for it's simplicity and nostalgic experience, and I enjoy Roblox's massive variety of games of varying genres to pick from. I'd like to see both communities be able to coexist with each other instead of going at it.
Well that's the end of my rant, hope you guys stay safe in these hectic times. Wash your hands!