As someone who loved watching Arturas play for us, and is also a Bulls fan, this breaks my heart, but it is an absolutely necessary move. He did nothing right for the Bulls.
In the wake of the unmitigated disastrous works of gar pax berg(honestly, how could they possibly think replacing Thibs with ******* puppet fred hoiberg was even a remotely good idea?!) the organization had a chance to reorganize and recharge. But Arturas did a piss poor job.
He seems to have been successful elsewhere in the league, but in Chicago he couldn't make a right move to save his life. Sinking so much faith and money into obviously damaged goods like lonzo ball was a FATAL mistake. Jesus, what was he thinking with that? It's bad enough lavar conned the lakers into taking him third in the draft, but how could Arturas let himself fall for the ploy?
There was a part of me that had hoped, after the season, he could convince Dan to do what the lakers couldn't and step away from UConn for a shot at the NBA. If that had worked out and turned out well it could have possibly saved his job. However, it's probably best to just rip off the bandaid now. It's time to deconstruct everything and start again in Chicago.
Good luck to Arturas wherever he ends up. He's smart, resilient and resourceful so he'll land on his feet. Just wasn't meant to be in Chicago.
edit: also, I've heard the Reinsdorfs say "this will take time, but we want to get it right" many times before. Sell the team.