I've done my best lifts in a meet, especially the deadlift. I've deadlifted more than 30 pounds more in competition than I can do at home in my garage. There's something about competition, with adrenalin flowing, that brings out the best in people. Especially if you are in a competitive flight.
In addition, it gives you something to train for. If you know you have a competition coming up you tend to train harder and focus on increasing your lifts.
Everyone has their reasons, and like Mark hinted at, if that is the view point, whats the point of anything? Its really an individual thing I guess.
My thoughts (from strongman comps, not PL)
Makes you get out of your comfort zone; which in turn makes you better. Deadlifting 500 in your garage is different than at a meet where you have spectators, pressure, seeing other lift more, worrying about failing in front of folk.
Lets you see where you are at; I started PL in my garage, my lifts were average but it wasn't until I started competing and seeing "whats possible" that I made leaps and bounds. Seeing someone deadlift 800 when you struggle with 405 really opens your mind.
Competitions push you; I don't know if this is a PL thing but in strongman (and also I don't know if that was just our group) but on max lifts we would go for a personal best, 5-10 maybe more, above our gym lift. Which is like your point, if you know what you can lift, why do it? so I guess the key is to BEAT what you know you can do, at risk, or else I guess you are right, why bother if you are going to play it safe, but that comes full circle back to the "individual".
Its enjoyable.
I was/am very shy. I could never of pictured myself doing that, but I did, before getting injured I did 15 (Missouri strongest man 2013 I think I nearly had two panic/anxiety attacks, vision went, felt shaky/nervous and I felt dizzy before two events) so doing the meets helped me in that way which was very valuable.
I was a crap lifter, but can no longer lift at all due to injury. Would have been nice to know what my best lifts actually were on paper as I can't remember exactly. Not that a 260 or 270 bench is anything special, or a 165 press, but I honestly can't remember, only about a 10 lb range. Figured I'd do better one day, but that might not happen. My buddy benched 315 which he worked hard for, but everyone calls bullshit as his ass is always way off the bemch. Competition would have fixed that. So chalk one up for posterity.
I get the impression that Matt (OP) is about 13.
I think the primary purpose of powerlifting in general and powerlifting meets in particular is to ensure the hegemony of the cisgendered patriarchy, to perpetuate the outdated gender roles that enforce this oppressive domination and subjugation, and to cement yet another area of the universe under the thumb of regressive white privilege or something probably.
You all have confirmed my thoughts - you pay money to make yourself feel good.
This reminds me of mud runs where people pay money to roll around in the mud so they can post a picture on social media - ha.
I'm not someone to judge what others do with their time & money but I'd like to point out to compete you have to have a chance of actually winning.
What's ironic is people training to compete in strength competitions actually make themselves weaker by trying to make a certain weight class.