Actually it's not like this. On FOSS when there is no manpower distros need to make a choice: supporting the software themselves or pick the maintained solution. So when upstart developed slowed down, by other words Canonical pulled resources from it, it was when they made the decision to switch to systemd.

Also the cost of maintain it and adapt applications who are tied to systemd is much more larger than adopting syetemd.

The only viable solution i'm seeing right now is: Use a mainstream distro with systemd or switch to other one which maintains their own init system like Slackware or Gentoo.

It's (slowly) becoming impossible.