Because you got a house and a nice ride. People tend to believe one if there is a result that they are seeing. Some of them hesitant cause they are still at doubt during the time they are being informed of it but now that they see you with achievements that you have made. The reality speaks when they asked you again for help. Also help them, its not that they throw you out before but even so still help them with all you can do especially they are still your family. Resentment isnt something good ones feeling.
The reactions you get from people or certain circumstances shouldn't change you negatively. If you a generally a good person, then be good. If it was your desire to aid them in the past, you should by all means do what you must but, perhaps with a priceand a little much stressful this time. At least, you've got to make them understand that opportunities aren't left hanging around for them to ride on at anytime. It's slippery and slips away at any point but, I don't really blame them for doubting. Besides, your meant to do your own research before going both feet deep in and looking out for some proof could be that for them.
Family success is actually for all and so, it pays even you @OP to carry them along in your engagement and exercise caution where need be.