There was a time
If I am not mistaken, when Elton John wasn't interested in getting hitched to his partner. Then the law changed in England, and he thought differently, even if it isn't call 'marriage'. And even earlier than that, I remember when he came out and his songs weren't played on the airwaves for more than a year, and he just kept on keeping on. All this to say: it seems that Elton does what Elton wants to do and doesn't concern himself with what other people think. And there is something else to consider: many musicians think of themselves as being beyond politics. That could play a factor too. But above and beyond all this, I bet the real reason he played for Limbaugh is that its all about show business, and John's spending habits are legendary.
If you are going to play for a homophobe, at least make him bow and scrap by paying through the nose. Big time.
Be the love you seek.