My suspicion is that Jory signed up simply for the glory of being a legendary Grey Warden and hero, but the reality was too hard for him to accept, as was some of the terms and conditions that come with wearing the uniform and being invited to the parties.
Duncan probably gave him a few chances to back out in Highever, but Jory simply ignored it and Duncan was so hard pressed for recruits that he couldn't refuse a willing volunteer, even if he was ill-suited for the life. From "The Calling" we are supposed to infer that Duncan chose Daveth because he reminded him of himself at that age, except that Daveth was fine with being a Warden whereas Duncan initially tried to run away... so it's possible that he thought Ser Jory might rise to the occasion and mature into the role and become a great Warden, much like he did?
Plus we get to see this from Duncan's shoes in Awakening, when we're forced to recruit people because we literally have no-one else left. Oghren's a drunk, but we know he's a great fighter and Sigrun already accepted a way of life that involves dying in the Deep Roads, so they'd make decent enough Wardens. Nathaniel is a strange choice as he initially thinks of it as a punishment, but he can find a sense of purpose in the life, if he embraced it.
On the other hand, you have Anders and Velanna, who are absolutely terrible candidates, since the former just wants to escape the CIrcle and the other just wants revenge. Anders and Velanna are the "Jory's" of Awakening, even if they don't back down from the Joining Ritual. After all is said and done, Anders runs away the first chance he gets, while Velanna is implied to leave either due to resenting the Warden for killing her sister, or leaves to join her.
At the end of the day, Duncan took who he could get, just like we did.
Regarding Fiona being Alistair's mother, I have no clue why people think that makes him a liar, since he still believes that his real mother was serving girl that Maric knocked up. Nor does it make him a hypocrite for being unable to break up with non-human Warden, as he has no clue that he's half-human himself.