When Sans said what if there's nothing to remember, I litteraly screamed YES!!! It just like Flowey said "I gave them the key and nothing happened. Why?" Easy. Just simple. The trigger is gone. The memories are gone.
Gaster got earsed and took with him all the memories and triggers. You cannot remember what doesn't exist anymore. You cannot trigger what doesn't exist anymore.
I have been reading this comic since early 2016. Literally the eyeball explosion “arc” (bc lets be honest what even was the cohesive plot of early hand plates? Not complaining I’ve been here for years now but HAH!) - which I’m pretty sure that First panel for the idea started in 2015 but like semantics- I FINALLY spent 10 minutes to feature the whole story. It took me 4 years. 4!!! Goodness freaking gracious, hopeless. I. am. hopeless!