Iran was fully abiding by the JCPOA (Obama Iran deal) until Trump pulled out in his first term. Trump hates Obama so that was entirely out of spite.
What is surprising is how co-opted the Biden admin was by Israel, that they didn't even bother to even consider reentering it despite it being a Democratic party "win" when it was first announced.
No, they tried to negotiate a new deal, not go back to the one they had agreed to. Why would Iran trust any new negotiations?
Iran was naive enough to trust the US twice in the last year and HAD THEIR NEGOTIATING TEAM BOMBED! I'm shocked they even trust the US to hold up to the deal they signed today. I'm guessing US concessions on frozen assets was just too much to pass up.