Because you'll still have customers on version 1.x, who will still expect support and refuse to update for <reasons>. It's not that it's impossible but it imposes an additional burden on the development team, which affects how fast you can add features.
That's why our team at GigaCorp has switched to not using minor version numbers. In the past we had customers who expected continuous security updates without updates to the minor version due to some internal policy. All of our new products use 0.0.x versioning where x is incremented for each release. This way we can easily push out new releases and our customers have no reason to delay updates.
But that's the same with 0.1 and 0.2. You will still have users in 0.1 who will expect support and refuse to update.
Unfortunately irrationally difficult customers are a bit like death and taxes in that sense, but "We have a new version with some minor fixes that you can use" is generally an easier sell than "We have a new version with some major changes that will completely disrupt your workflow".
This is true no matter what you name your versions, I don't know what you are saying.