Because it's easy for Jirren to already achieved that shyt... They (U11) is the TOP tiered MORTAL universe according to all the destroyers/gods... U7 is ranked the WEAKEST....
So when goku pulled that stunt showing them the SSB form for the first time they was shocked. I mean these dudes barely interact with beerus and champa on any level so they haven't kept their ear to the streets... So they started to panic because a lowly saiyan reached the SSB form... it's shocking to them. and the UI form was something not even GODS can easily achieve so it's a milestone for goku to get to THAT level and NOT be a god coming from the weakest universe according to them... That why Rat Destroyer and Clown destroyer was plotting on the low since then trying to sabotage them...
universe 11 might be the strongest of the competing universes, but they're not #1 or they would be exempt from being erased.
jiren's power has caught some of the god's by surprise as well. but they'd heard rumors about "the mortal who had surpassed a god of destruction", so they were aware even if they'd never seen him. the first thing they heard about goku was "yeah... THIS is the idiot who got us fighting for our lives". they didn't know he'd actually given everyone a chance to survive. or that he was GOKU... until he started handing out fades during the prelims.
and the god's aren't plotting on goku to sabotage him because he reached SSB and UI. they explained why they were doing it. take out goku and universe 7 probably loses as a result. and let's be real... are they wrong?