Why this u-boot fork detached from main development team?

[ponyatov]

Looks like github.com/u-boot/u-boot is a mainstream project?

Why this fork was detached, and don't contribute to official main branch?

[valinskas]

My guess due to a lack of time. Doing patches the right way and redoing them till it is done right takes a lot of effort.

If you feel like you might try taking changes and try pushing upstream via pull requests.