Maybe because jealousy is a human trait all people have. They would be jealous even if you were a stranger. Getting what you have is not just a matter of doing everything right, it's a matter of having the capability to "do everything right" which not everybody thinks is a piece of cake and it comes easier to some people than to others, maybe because of mental differences.
This might sound far-fetched to you, but if you want to lessen their jealousy, I recommend sharing with them. Talk to them, invite them over(and don't be pretentious or compare them to you or flaunt what you have!), give them a gift or money now and then, acknowledge them for what they have done for you, and encourage them in reaching their own success. Maybe they feel jealous because they do not share your perspective of it being easy anyone can do it, they may think they will never have what you have.
That is they tend tO think they should earn the same attention like u have.
It's because they want what you have. They are usaually miserable people and want to " rain on your parade." having said that most jealous folks never worked hard for anything. I've noticed that they take a more dishonorable route in life to get what they want. Seeing true success is usually a problem for jealous people. Nothing is natural and easy for them because they live on conflict. You just become the center of their chaos.
I get so fed up of working so hard and for so long and reading self help books to enable me to believe in myself and reach my goals... and then someone jealous comes along and destroys years of work within a few months. I also get fed up of hearing that for some reason it was "easier for me" than it would be for them. No it isn't. I just wanted it so much that I got over the criticisms along the way, the nay-sayers, the people who told me (for example) all my life that I couldn't sing. I actually not only taught myself to sing from scratch (I was awful at first), but I had to get past the idea that I was not talented and would never be able to do it in a million years. Does that sound like an easy thing to do? Well it's not. People who are jealous just make excuses because they are cowards who haven't got the guts to fail. So they never learn because they never try. You remind them of how pathetically fearful they are and that's why they have to take things from you- to hide that fact from themselves. No one on this planet has it 'easy'. Jealous people miss the big picture of why the other person has something they don't. It's this delusional thinking that hides the METHOD necessary to attain their secret desired goal. If they would only pay attention to the reality, they could discover how to attain it for themselves instead of basically turning into a bully.
simply said- because they want to have what you have. And never got it , so they must torment the one they love. then get away with it! so dont go there ok. be strong and have a turtle shell lol.
They are jealous and small minded. If it is sibbling you are dealing with someone that had plans of killing you when you were only 4....
You answered your own question: Cause they are jealous.
Try being more modest.