Unlike the source material that informs it, death in comic book movies is a pretty permanent thing. Yes, there have been moments where characters have seemed dead, and were revealed to have only been a little big dead, or where circumstances combined to give them a ridiculous Lazarus-like resurrection that only worked if you sort of ignored all of the questions in your head, but for the most part, if someone is intended to be dead for the sake of a story, they will remain so in the movies.
The problem with that of course is that comic books rejuvenate dead characters every couple of years, and nobody really bats an eyelash at the idea because it means that beloved heroes and villains alike can be mined for the sake of better and more entertaining stories (rather than inventing new, sub-par baddies, or going with C-listers).
Movies with a kill count really cannot do that without someone pressing reboot, and fans are rightly now becoming a little cynical of that whole start again culture, and unfortunately, because film-makers have to fill a quota of drama and excitement, characters tend to be killed off all too quickly.
While those flashpoints - whether the tragic death of a heroic figure, or the justified death of a villain - are satisfactory for the film, the source is so bountiful that it tends to mean they leave with a trail of missed opportunities and un-explored storylines, and fans are left wishing they'd been a little less fatally dealt with.
And unfortunately, that happens quite a bit...