I think it's a combination of things.
The first is the overriding belief that abundance and opportunities are "limited". Therefore if (A) gets something it is at the expense of (B) having less. The reality is there are more millionaires and billionaires today than ever before. One is only limited by his or her imagination and willingness to do what it takes to accomplish their goals. The "blame game" is too easy to play.
Secondly very few people actually "welcome change". Very often it is forced upon them and they resent it. This goes for just about anything from "new procedures" at work, a new boss who demands more, long held traditions "Instead of having turkey this Thanksgiving I thought we'd have chicken pot pies." WTF?! LOL!
Now if someone is going to lose it over changing a menu item you can only imagine how some people might feel about being (forced) to compete, share, or associate with others not of their choosing. The resentment is even stronger if one believes the new boss or associate was given "an unfair break" of some kind in order to get where they are. A male dominant occupation suddenly has to be schooled on what is considered "sexual harassment". They aren't free to joke/behave the way they use to and this would apply to any situation where a minority of any type or someone of a different culture joins the team.
People usually don't "embrace" change. They become "accustom" to change (overtime)!
With the passing of each generation the change of "today" becomes less of an issue. Fifty years from now people will wonder what the big deal was over Obamacare or Marriage Equality. There was a time when people were upset over fluoridated water and interracial dating.