One of our posters wrote this out and seems to fit the situation....
Richardson wasn't a key cog in their defense.
In 2015, despite his Pro-Bowl talent, their overall strength along the defensive line, and their clear needs at other positions, the Jets went out and did the most Jet like thing imaginable. With the 6th pick of the draft, instead of addressing one of their multiple areas of need, they went with the "best player available," and drafted Richardson's clone, Leonard Williams.
When Williams turned out to be everything he was advertised to be, they were left with three dominant linemen, who play, essentially, the same position. It seems they could have chosen to switch to a 4-3 defensive scheme, but the Jets, being the Jets, stubbornly stuck with their 3-4 which left Richardson as the odd man out. They tried moving him around, but he never found success out of his natural 3-tech position.
So, what you really had, was an extra cog with a starter level price tag, and a bad attitude about how the Jets had treated him over the years. Jets were moving on from him one way or another.
I think this is why he will excel with us.