The easy answer is this is what happens when you choose a quarterback in the first round and miss, but it is deeper than that. Tomlin refused to trust Pickett. He wanted to replace Roethlisberger with a veteran. They should have re-signed Rudolph and let him compete with Pickett for the job last year. I don't think Pickett would have been a long-term answer, but he could have been their bridge guy. Tomlin wanted a veteran and the only way to get Wilson to sign was to promise him the job. Pickett got pissed about not even being allowed to compete for his job. Remember, late in the previous season, Pickett underwent a surgical procedure to try to get his sprained ankle to recover more quickly and they never let him play again, so Pickett wasn't being entirely unreasonable.
The smart thing to do then would have been to talk Pickett down. Even if he won't listen at first, let it sit for a week. The Steelers traded him for peanuts and replaced him with Fields, another failed project. That led to a wasted year of Wilson and Fields and a quarterback cabinet that was completely bare. They could have addressed that more aggressively. They had more money and a better supporting cast than the Seahawks and Darnold took a deal with an easy out after one season. Instead, they decided to wait on Rodgers, which has been an embarrassing shirt show.
This is becoming a trend with Tomlin, becoming enamored with washed-up quarterbacks. He did it with Michael Vick, then Wilson. Now it is Rodgers. Hopefully, someone in that organization learns their lesson and they make better decisions next offseason.