15 years later and in proximity to a major life change, which is a reasonable time and situation to consider that his priorities might've changed.
What major life change? His engagement (it's been a while but as I recall, he was already promised the captaincy by the time of his actual wedding)? Why would it make sense to give him a ship when he was engaged to a woman on his current posting?
It makes far more sense that he was occasionally offered commands we didn't see, and he finally decided to accept one.
In fact, we don't actually have canonical proof of an offer, as it could have been him requesting a command.
Does that really matter though? Assuming he requested a command, he got it, so obviously there was a command available for him.