1. They can't afford bitcoin.
2. Too late to the trend, they are jelous of peoples who get into the trend long before them so that those peoples earn more than them.
3. They want to make peoples leave bitcoin and chose other digital currency which they have bought with the intention to raise its value, greed are disgusting when are too much that you do anything to get what you want.
4. Etc you can think of.
So don't mind those peoples, only sell your bitcoin or buy it when you see profit.
Well, people hate what they are afraid of. They are afraid that bitcoin will continue to increase its price and they would continue to be living the way they are living their life while some of their friends are already enjoying the profits that they are getting from bitcoin by working last year to get some. You are a little late when you are just about to start earning bitcoins now because it has skyrocketed already but you are not too late.
In psychology, when someone succeeds in something that you don't care about, it's alright. For example, if your friend is succeeding in photography and you are into singing, you don't really care. But when your friend is succeeding in singing and singing is your thing, it's really hard to not to feel envious about it because they are outshining you. This is very hard especially when you're working on it for a really long time and then someone comes along and just made it to the point that you've never been to before.
The thing, though, everyone wants to become successful financially and bitcoin users just went ahead of almost everyone. Another thing is that it's the millennials or the "kids" that has been earning a lot from bitcoin because they are the most tech savvy of all and the previous generation is pretty mad about that.