I had the same problem for the longest time and it was being I wasn't willing to play for big stacks when I needed to. Especially in the middle stages where stacks are getting shallow and it's getting closer to the money.
When I found myself struggling to make it deep in mtts, I was trying to justify holding on my stack as long as possible. You might tell yourself the same thing "I have 40 bbs and only 35 players from the money, I can play tight and make it there."
And maybe I did, maybe I didn't but, whenever I did cash, it was very rarely with a big stack. Majority of the time, I had a few big blinds left and a min-cash. Then would come everything in hindsight that I should've done that I didn't.
So, I decided to switch things up and start playing for big pots. If I had a big hand, I went for big value with it pre and post flop. I 3bet my strong hands a lot more. I was more willing to get it all in preflop in close
equity spots. I was willing to 50/50 flip with AK for 50 bbs (100 bb pot). Or get it in with 25 bbs and KQs in SB facing a MP open and 2 cold calls when it's on the money bubble. Etc.
Of course, hand selection is important and i wouldn't be 3betting jamming A10o for 50 bbs in the same scenario I would AK. The main factor I was more willing to put my mtt life at risk in spots where I felt I had an edge or was slightly behind to build up my stack because I understood that a having a bigger stack was going to get me much deeper in mtts than not. It's not impossible to win an mtt with only 10 bbs after the bubble, but I would have a much better chance building my to 100+ bbs 50% of the time than having 10 bbs 100% of the time.
On the plus side, when I started playing for bigger stacks, my confidence in my game grew a lot. Even though I was putting myself at much more risk and busting out more, I stopped regretted my decisions. You would think that someone busting out with AK and 50 bbs would be kicking themselves, but the opposite is true. I was regretting the times I wasn't making these plays, when I was playing too tight and not making it deep in mtts. For me, the fact that I can play and not regret any of my decisions, no matter the results, is huge in not only building my confidence at the tables but it allows me to focus on things that are important in the game.
With all that said, I think it's important to figure out what works for you in MTTs as well. While I don't mind risking 50 bbs with AK, there will be a lot of players that will say it's not necessary to do so. And they could be correct with their own strategy. Maybe you don't feel comfortable putting that much at risk. Maybe it's more important for you to cash first and then make the big plays. No matter what you do, have a plan on what you're going to do in situations. It could be as simple as "if I ever get down to 15 bbs or lower, I'm going to find spots to get my stack in, not matter what." Maybe plan to steal, re-steal, and 3bet more the closer you get to the money bubble to take advantage of the tighter players.