Why don't trannies admit they do it because they were incels?
Probably because it's not true.
You can look at photos of trannies before and after transitioning and all of them were incel-tier when they were male.
Oh? Most pre-transition pics of trans ladies I've seen look like regular guys. Some even look pretty handsome. Heck, I think I used to make a fairly attractive dude myself, if a bit overweight. I mean, as a teen I once had a girl very obviously try to get me to ask her to a dance, so I'm pretty sure that means I wasn't an incel.
But incels have serious body image issues so even decent looking ones think they're super ugly. I'd feel sorry for them if they'd quit it with the raging misogyny and other kinds of hateful bullshit.