The snapshot worlds won't load on my computer, I download them, and then I click play, it loads up the MOJANG page and then crashes.

When I go into Minecraft and go to snapshots, I am able to download them, but I don't see all the available snapshots out there, only certain versions of them. for instance, 18w20c i think was one? i only saw 18w20b not a, or c, or any others. And when I try to get a new version, nothing seems to work, because it lets me download it, it lets me click play, but then it goes to the normal MOJANG loading screen, but unlike with other versions of MC, it crashes! I don't know why this happens, I was able to play some other snap shot worlds, like 18w11a or something close to that, and I still can play that version of snap shot worlds, but I can't play the more recent ones. Please help with this issue, or at least assure me that when the official 1.13 update comes out I'll be able to play it, because I've been waiting a LONG time for this update!