Because non-developers deal with versions. Sure, programmers use zero-indexing because it makes a lot of common things a lot easier, but I can't imagine anyone

Because non-developers deal with versions. Sure, programmers use zero-indexing because it makes a lot of common things a lot easier, but I can't imagine anyone expecting that to extend to the regular world where the first item being 1 is ingrained, and makes more sense given the use. For this reason, 0.x versions can make sense - they serve as a good flag for 'this is pre-release', because people expect version 1 to be the first released version.