28 years of banking and getting rejected!

So I have been a client of FNB from the age of 22 so its just of 28 years in which they have made money off me, I have a very large saving purse with them and my car in financed with them currently. I decided to ask them to give me a home loan pre-approval, because I managed to get a few from some other places including Ooba, I thought let me approach my bank directly. Guess what? I was rejected! rejected a pre-approval, I didnt even ask for a LOAN! just a pre-approval! and I am told that I could not be given a pre-approval because of 'insufficient disposable income' How is it that every other place can give me a pre-approval but the bank I've been banking with for more 28 years cannot??? Everyone says go to the bank you bank with and you are sure to get a good deal, really! it that REALLY true? So yeah I dont think I am going to be banking with FNB for much longer after this kind of rejection!