That's an interesting hypothesis, I'm not sure about it.

OpenRCT2 is a re-implementation of Roller Coaster Tycoon 2; a business simulation game in which you build theme parks. It's similar to TTD (which was a predecessor from the same developer), but with much less focus on logistics and more focus on artistic creativity. OpenMW is a re-implementation of Morrowind, a fantasy roll-playing game that, by modern standards, is a bit unforgiving to beginners and doesn't have much hand holding. All three are from the 90s and arguably nerdy.

On the other hand, it's my perception that minecraft has a mature and nerdy following too. Lots of kids play it as well, but there seems to be no shortage of tech workers who are into it. I think minecraft's redstone has more to offer a nerd than any of the three above games. And there is a mature modding scene for minecraft, making the game even more technical. I think/hope throwaway290 is right, that minetest will get much more attention from capable developers once Mojang strangles the life out of Java Edition.

Could it be that network effects are much stronger for Minecraft? Morrowind is a single-player game. OpenTTD has network play but I have always played it solo and I suspect many others are the same. I don't play Minecraft but from what I have seen, cooperative play is a big part of it. Players may be less motivated to work on a FOSS alternative when they know that they would then also have to convince the community to move to it, which is much harder. Same way it's difficult to build a real FOSS alternative to WhatsApp, for example.