The reasoning behind Spidey losing his mask at the end of each movie has been explained by Sam Raimi a couple of times. Unlike other superheroes, Spidey's mask covers the entire face, meaning that aside from the voice of Spider-Man, the audience would not be as connected if they couldn't see what he was feeling and going through.
In the comics, you're able to dive into Peter's head through thought bubbles, or things of that nature, but it's gonna be really hard to pull that off in a movie. Which is why Spidey loses his mask, or gets his mask torn half way so that you can see his expressions and really connect with what he's going through at that moment.
I know alot of people hated Spider-Man losing his mask in the 2nd movie at the train part, but do you really think that the scene where he stops the train would've been as powerful if his entire face was covered? Sam had to get rid of his mask so that we could see that Spidey was literally pushing his strength to the edge as he tried to save all those people.