When you are a ruler and the last (adult) noble of a clan in your empire dies you inherit their lands. So eventually you'll end up with plenty of towns. It would be nice if it always gave you the option of making yourself the owner of the town, but it doesn't.
Currently (as far as I know) there is no way to bribe someone to join you by offering them a town anyways unless you have level 300 stats in trade. I've never been able to offer a town. Also, when you get to level 125 in skill level for leadership, you can pick a perk that gives you an extra 5 party size for each town you own. For this reason, I never give away towns I own. In my current campaign I own 9 towns, which helps my income, but also adds an additional 45 to my party size. That can be a big advantage. Generally, once I get a clan to join me I give them one of my castles so they have a base & it also improves relations. But I never give away my towns.