This isn't just Disney, mind you. Animes have a ton of it. Various video games, other movies that are not related to Disney as well.
It's the number 1 kick starter for any "amazing" character. It is the most common thing used when making any character. Which is why most people are drawn to it. They are familiar with it all too much that they use it. Even if it is twisted up, it's kind of like a reflex to some people to explain why their character doesn't have one.
Especially on FH, having an actual parent that is still alive, still active, etc is REALLY difficult to obtain. Yes there is always the whole: parents left option, but if you say "my parents are dead for [insert reason]" it's 1: a conversation starter [even if they are seeking attention], 2: A way to give their character certain tragic traits [extreme determination, motivation, want for revenge, closed off and doesn't speak much, more hostile, the want to be someone good, or even bad, the possibilities are limitless!] Yes there are always other ways to achieve these traits, maybe they were born with it, maybe they had it thrust upon them by some tragic event. However, to fill in blanks without spending ages on making some elaborate story as to how you are who you are now, parents death will always come up first.
It may be annoying under some [okay maybe most] circumstances, but what can you really do about the matter?
