bulimia is pretty chaotic. I honestly used to wonder the same thing, but having suffered from bulimia on-and-off for long enough now to experience the health consequences and the crazy weight cycling (sometimes I lose weight with purging, sometimes I gain. It's a total crapshoot) I've come to understand why someone would not pick this for themselves if they had the ability to. I've also come to understand that being bulimic does not make me "immune" to weight gain, like I used to think it did. It really throws your hormones out of whack and makes weight loss harder and harder as you age, at least for me and my sluggish thyroid. If I'm in a b/p stage, particularly if my body weight is low and demanding calories, I will b/p all day. It's exhausting. Sometimes I'll just fall asleep after a huge binge without purging because I'm so freaking exhausted, and, ultimately, I give in to eating and not purging regularly because it's the only way to end the cycle. Eventually, I gain whatever weight I lost back (and then some) and realize that I could have saved myself a lot of pain, health consequences, and a hell of a lot of money if I had just given in to binge eating minus the compensatory behavior. Seriously, like tens of thousands of dollars that could be in my bank account right now if I hadn't been spending $100/day on food alone for months on end during my worst period. Not to mention bulimia makes you malnourished/weak, bloated, constipated, gives you chipmunk cheeks, and generally leads to a very "skinny fat" kind of aesthetic that messes with my body image even if I'm at a lower weight. I dare say that, at this point, I would consciously choose being heavier over being bulimic, although I don't really get to choose. Obviously the preference would be lean and also not bulimic--but again, it's not really a choice.
Also I think some people just genuinely hate throwing up enough to not want to do it/aren't physically able to do it
Fr, purging in and of itself feels chaotic af. After a massive binge, the panic and the guilt sinks in, I see how much my stomach had expanded and it's like the toilet is fucking luring me in. I can't stop thinking about needing to do it, until I do. As I'm doing it, I'm playing as much sounds as possible to drown the gagging. And my mind is constantly thinking about that one picture of that girl who unfortunately died during a purge. I keep thinking, please don't die, please don't die. I do one or two rounds, because flushing can quite literally kill you instantly. Then I just sit there, tears and puke on my face. It's not pretty. It's disgusting and I hate having to do it. I've purged in public toilets, family members' houses, friends' houses, in a trash bag, in a bush, behind a fucking dumpster. It's also very common to get toilet water splash back in your face or eyes like a big fuck you from the universe. And also the consistent tonsillitis isn't fun either. I completely understand why someone wouldn't want to purge.
It takes more self control to NOT purge and in that, I applaud binge eaters. I'm too much of a coward to sit there and face what I've done. For me, a binge/purge episode can last as little as 20 minutes. I eat the monolithic amount of food quickly, then immediately purge and straight after that with no break I clean everything up; the puke in the toilet, the trash from the food, all of it. And I dispose of everything, then act like it never happened. Then I obviously get hungry again and the cycle starts again unless I break it with my restriction periods (which I prefer for obvious reasons).