Why do people wait for Green Card before buying home in USA ?

We are on the H1B visa in the United States from past 3 years, applied for the green card and planning to buy a home (prices are low now and also benefit the economy if possible), but the question arises - why do people wait to buy property until they get the Green Card ?Why do people wait for Green Card before buying home in USA ?
Some people don't buy a home for reasons not related to visa status, but more related to their job situation (i.e. they are afraid of losing it). If you have an H-1B and are in the GC process, you still should be able to find a bank willing to cooperate. They will normally ask for a letter from the Immigration attorney stating that you are in the Permanent Residency process and, although not guaranteed, they don't foresee any issues with the process.Why do people wait for Green Card before buying home in USA ?
Because H-1B is a temporary non-immigrant visa. If you are terminated and lose your status, and cannot transfer to another employer, you will have to leave the USA immediately (there is no grace period). This is why people wait for a green card or at least more than 180 after filing the I-485. Especially in this economy, I hear every day from people who were terminated by their H1b employers and have to leave the country.
Because if you are on a temporary visa it can be very hard to get a mortgage company to give you a loan. Yes it was easy before the crash but now, it is not.