Because he’s Bra’tac. 
Yeah, that was convincing, Jack. 
“Nirti’s been working out.” 
Not so much, Jack.
Nice tense moment.
Yeah, definitely get down.
Indeed…
Yeah, genius.
And actually, neither of them are “Earthans”
Yeah, this isn’t suspicious at all.
Or even “Earthlings”…
Very distracting blue filter there.
Oh eewww…
That was a quick alarm.
And not a good place to be.
Eww, that queen is really nasty.
Again, EEEWWWWW!!!
“It is essentially an asexual process.”
“Is that why you guys take hosts?”
Oh, Jack.
But not an unexpected reaction from Jack 
Question, then why did what’s-her-name need Daniel in season 1?
Think it had more to do with making them compatible with human-based Jaffa (like Hathor turned Jack into). Either that or a retcon.
I vote for retcon
Oh, that’s not good.