there is only one reason players fail at mtt but not on mttsngs and thats simply they are too tight also they probably lack understanding of many concepts , if i tell you to be looser it wont help you either since you probably wont know how to do that. There is a lot of misinformation online or on videos , you wont get proper answers and even if they are correct you probably wont understand what they mean , playing tight works on mttsngs but not on big field mtts.
I had the same problem but now i can even do 3-4 final tables with the chip lead on 20 mtts with a 2.5k+ field size , to win an mtt you simply have to become a lot looser which means having a bigger calling and raising range from early to late pos and try a lot of steal moves from late position with a much bigger but still legitimate hand range , if you dont do both you wont win small pots which are crucial for mid to late stages to keep your stack up , also you will lose the chance to hit that unsuspected big hand to double you up.
Another important thing for mtt is pot control , if you dont do that well you will get trapped in very tough decisions and lose it all , since mtt last for so many hours its very important to have a plan how to play each hand and pot and survive every single of them , trying to call to much in a pot who will turn big in river or turn w/o knowing the answer will kill your chances.
Mtts are like small pot small pot big hand small pot small pot and so on..... sometimes even if you are looser that big hand still doesnt arrive and you can barely keep up so you must have some short stack plan and understand stack sizes as well , the less your stack is or your opponent's the more you will have to bet to the max hands like tpmd or even second pair.
Simply there are too many concepts to cover in one post but the overall idea is the same *play looser have the skill to hunt all the opportunities that arise* i recommend you reading all hands revealed by gus hansen and poker tournament formula by arnold snyder , its a great combination that helped me a lot.