This is all about circumstance.
Elton didn't meet David until late in life, so why should he be denied the chance to be a father? He could well have had a child when he was married to Renate, but it would have been a bit of a fluke, and a band aid child too.
Because he's too old.
It's ego, pure and simple. When his child is 15 he will be 80 - if he's still going. & to say he'll be financially secure is true - but there's no substiute for parental love. Money is not the be all and end all.