Hi Jbird,
It is very difficult to guess why. You could ask them directly but you will never know if that was the true answer. Sometimes people do not know all the reasons why they do (or do not do) stuff. Sometimes those reasons are pretty twisted.
I apologize for being too sharp, but I think unless it is important for you to establish a more sincere relationship with them, I would let them go. It is not worthy. For the purpose of your plan to get out of the financial problem you are in, they should be dead to you.
Nobody is to pay you back what you did for your mom. Inheritance legislation does not regulates that I believe, everyone comes to ask for their share when their parents die, even those who never stopped by to say even hello when their parents were sick or needed help. We have seen this thousand of times, and it happens everywhere in the world.
I am not sure if I understood well your previous post, but if the house of your mom is under your name, so the house is yours, just keep the house as yours, sell it if you need , keep the money as you need.