Bowser is just lonely and probably has nothing better to do, and it is also apart of his plan of taking over the kingdom/world. If he marries Peach he can be king of mushroom kingdom and Peach cant do anything really, But i have one question how did Baby Bowser come to be???
Anyways, to answer your question I refer to Paper Mario. In Bowser's diary, he writes about how he wants Princess Peach to like him by showing off his power and flaunt his abilites. His pride however also causes him to become blind to the fact that the Princess does not like him, and he feels that Mario is the true bad guy for always foiling his attempt at attracting Princess Peach.
Is it my question your relating to. If it is then I don't see the answer to it, but I would originaly think that Bowser adopted Baby Bowser, But who in the right mind would let Bowser adopt a kid???
because that him when he was little and he didn't adopt him that him when bowser was little and baby bowser was the seven star children and peach hates bowser and don't like him because peach is in love with mario like daisy in love luigi when baby daisy was made in mario kart she scare baby luigi and baby luigi like her but he scare of her and baby donkey kong he cute and adorable and baby yoshi was one of the seven star children