Whatever the merits of the rules themselves (which I think are estimable), the OSR "ecosystem" is buoyed up by a huge network effect. I would wager that just the list of official D&D modules from the 80s, all of which are easily playable in something like OSE, dwarfs the amount of support that's available for all of those other games combined. That's not counting the many many additional adventures, settings, rules addons, megadungeons, GM aids, etc. that have been created in the last 20 years for various OSR games, which are mostly cross-compatible. It's very hard to come in fresh and compete with that.