Why did not they add the features to OpenWrt trying to make it better?
Almost all the forks of OpenWrt die in months. Some lasted only few years. I am afraid that it is a wasted effort.
I think mainline openwrt runs on turris hardware now. From what I remember, the main feature of their fork is/was snapshot management through btrfs. Updates are quite lacking in general on openwrt, so I think it's good that they are doing something about it. Ideally, I would like to run a full distro on routers, and manage it through standard distro tools, now that we have reasonably powerful hardware (like the Turris).
OpenWRT development was stale when Turris started. Don't forget the LEDE fork was born out of problems with OpenWRT development.