Roblox has the ugliest design I've ever seen for an online game yet it's amazingly successful. What's their secret?
Free exploration, community and YouTube.
The way developers iterate on gaming concepts and allow players to be part of the evolution seems to be appealing.
Tower Defence games are one example, where there are many implementations.
The games evolve and change, sometimes rapidly, and the players and community come along for the ride. Then another new Tower Defence game comes along, a YouTuber showcases it, and they all go try out that one. Then the old game gets a big update, and they go back and try the old one again.
The games are often very similar to each other, or knock-offs of commercial games. They often use irreverent meme culture visuals and sound effects, which makes the games seem fun and disposable. None of it is taken very seriously, on the surface at least.
The key here is the community - all these games and their friends are on Roblox. They don't lose their friends if they switch games, and games are free to play, so their friends can easily join them without having to ask their Parents to buy the game for them!
When you look back at the early Roblox games, it's remarkable how primitive they are. However when you view todays games, it's equally remarkable for sophisticated and impressive the graphics are!
Being an open platform with user-generated-content it has content covering basically anything kids are interested in and can react very quickly to incorporate "content" from whatever is currently trending.
They've taken the Facebook / PHP "it sucks but we move fast and have a very low barrier to entry" ethos and applied it to gaming, aimed at a very young audience (my kids of 7 & 10 and all of their friends play it) and - with their horrific monetization - are killing it.
The "secret" for both those cases is likely that they were lazy and just used some low effort placeholder at first, then the game blew up and the style became too intertwined with the popularity to change.
Roblox looks actually ugly because it uses higher resolution assets without a common/appealing style to make them cohesive.
Most websites indeed looked very similar in 1996, but that was because of the currently accepted design aesthetics of the time, and had little to do with the browser itself.
However, ugly or not, most people don't care, and the gameplay itself was so interesting to its audience that it didn't really matter. Lots of things are more approachable and relatable specifically because they're ugly, and I think that applies to both Minecraft and Roblox. It's easier to imagine yourself making or participating in something that doesn't look like it took a genius to do. They made zillions of dollars and lots of people have fun with their games.
But that doesn't mean I have to like it.
Plus, that's what people are used to.