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. Does that really matter though? Assuming he requested a command, he got it, so obviously there was a command available for him.
Because major life changes like marriages tend to change priorities and cause people to reconsider other aspects of their life as well. In the eyes of Starfleet's personnel department (or whatever), the reasons for him previously refusing command may have no longer applied and so it may have been worth granting another offer if it was in fact an offer. Besides, any conceivable change that would have led to him having decided to finally accept an offer after 15 years of saying "no" could also have been a reason for Starfleet to grant an offer after nearly 15 years of none; it's equally supportive evidence for both sides. Unless it was literally arbitrary on Riker's part, but that doesn't seem like him at all. And you still haven't really said how it makes sense for Starfleet as an organization to keep making offers that they would have to assume would be summarily rejected. What reasonable person or organization would keep badgering someone with an offer after it's been rejected three times already? It matters because you proposed it as evidence for your side. I said they would've eventually stopped giving him offers that he would have just refused. You responded that we had canonical proof of at least one further offer as evidence that they wouldn't have stopped giving them. So then I pointed out that it's not actually evidence that they wouldn't have stopped giving them, because we don't actually know that they offered command as opposed to Riker requesting command. I was demonstrating that it doesn't automatically support your position.
Because Starfleet wants to put the best person possible in its free positions. If Riker is the best person possible, it makes sense to ask him on the off chance he's had a personal epiphany or reconsidered this time. Fair enough.
Captain is both a rank and a title in the Navy. The Captain of a vessel is its commanding officer. That commanding officer could be anything from an Ensign to an Admiral. In Starfleet, a small vessel like the Defiant may not need a Captain-by-rank to command it. A Lieutenant Commander or full Commander would have the necessary experience to sit the center chair.
The offers kind of dried up after Starfleet Command had a chance to watch Rascals and Generations. As much as I *love* the Sagittarius gang, it doesn't make a lot of sense to me that the commander of a 14-person ship should be a full 2.5-stripe captain.
Weird. I obviously didn't pay much attention to the figures in the 24th Century section of The Star Trek Chronology. I suppose I'd just always assumed that Picard's age was at least roughly the same as Patrick Stewart's. I do remember seeing some ST reference book that appeared during TNG's 1st season giving Picard's age as 45. I have a strong memory of thinking that seemed way too young to me, and he should've been into his 50s. Maybe that's what made me think that Picard was a bit younger than he was.