Just a thought

So based off of how many zombies we see in the movies, there would be like ten times as many ready to be found...

Also, say if it's an apocalypse, people might be dying faster than they can bury dead people, so that makes it easier for zombies

Well zombies are stronger than normal humans because they don't have that part of their brain telling them not to do something because they might get hurt from it. So they could easily get out of their caskets. And they could crawl their way out of the soil because I think the only reason a normal person wouldn't be able to is because of fatigue. But however if the ground is packed tight then that would be the only problem if it was packed tight enough that they wouldn't be able to claw their way out.

The soil would engulf them and they wouldn't be able to move their limbs no matter the slight super human strength they posses

Yeah that's what I was saying would be the only flaw