As Chuck Noll said, you can't make the club from the tub.
It's unclear whether Mike Tomlin has a spin-off catch-phrase regarding players not being able to make or stay on a roster, but it would probably be something like "you can't make the team if you get suspended for four games in a season."
Less catchy, but similarly poignant.
That fourth game was a Thursday Night contest, meaning the Steelers had a short week to prepare, and were granted a roster exemption by the league, meaning Saunders could stay on the roster, essentially in suspension, and not play in their game against Tennessee.
It was expected the Steelers would release either Leonard Pope or David Paulson, and the move to have Saunders hit the road wasn't anticipated. Paulson has seen his snaps increase on offense in each game, and has become the team's No. 2 tight end behind Heath Miller.
It appears he will continue in that role in the future.
Saunders is now free to sign with another team, but his release would also bring into question his level of fitness. Whether he's able to participate immediately is a different story.
Saunders was an undrafted free agent in 2011, signing with the Steelers with the label of having a high upside. He had four catches and a touchdown in his rookie year.