sometimes the answer to a bakashah is “no.” It doesn’t matter how many people ask, hashem still said no. Rav Ovadia lived a long, full life, and he didn’t deserve to suffer in his old age.
Well, if it was a given that every Tefillah made by 50,000 people would be answered, then we would have a serious hand up over HKBH. He wouldn’t be able to run the world the way He needs to. Obviously, some times some Tefillos cannot be answered as we ask.