He's not consistent enough. Conor has skills and with proper marketing and fight selection, he can look amazing. But, eventually, if a fighter is to call himself a GOAT or at least consider himself to be in talks, he's gonna have to go threw a slew of contenders, many of which are hungry for glory and have a variety or skills and abilities that vary from the norm. Until Conor can beat any up and comer and take on all challengers and win, he's not GOAT material. GOATS fight all types of fighters and come out on top all of the time during their reign. GSP and Jones (say what you will about his history) have emerged victorious and stood the test of time. Silva is a good candidate, too (at least for the time). Khabib may be well on his way. His body of work isn't quite as extensive as the others, but he's looking quite invincible. Strikers can't beat him, grapplers can't beat him, and even generalists haven't seemed to be able to beat him. If Khabib can get passed Tony, who I would consider an advanced generalist who leans towards striking, but has legit grappling chops, I'd consider Khabib as the guy that's heading towards GOAT territory.
Conor and his fans can parade around like Conor is one of the best, but eventually, someone will and have pulled his card before, and we've seen the results. Even in GSP's losses, he's never been thoroughly dominated and embarrassed. He's been beaten, and caught clean, but there was always an avenue for him to redeem himself. Besides Conor's earlier losses by sub, Conor has been thoroughly beaten twice, his last lost he was blown out. Conor isn't particularly early in his career to chalk it up to inexperience, either. He has some clear holes. Not that he can't fill those holes, but his trajectory doesn't lend itself to be the case. I could be wrong, but Conor doesn't seem to have enough time left to put off fighting every top fighter there is and coming out victorious all the time. Conor has to go on a legendary run, he'd have to take out Masvidal, Justin, Tony, Hooker, Dustin (again just to make a statement), Felder, and rematch and beat Khabib and then defend some times. That would be a GOAT worthy redemption story. Conor taking on fighters coming off of bad losses or settling grudge matches with opponents who won't taste a belt only to hope to catch the champ (whoever it turns out to beat) in the next the fight isn't the right answer.
Positioning himself for gold by avoiding the landmines will come back to bite him because eventually guys like Khabib or Tony or some other threat we haven't considered will rise to the occasion and challenge Conor. What will Conor do? Probably go on hiatus, joke about who is worthy or not, and then hint at retirement. People will note these things and if he's pushed into a corner and "has" to take a fight and loses, the whole cycle begins again. Conor can't afford another misstep like what happened when he became double champ, got stripped due to inactivity, and then jump into the fray again. Not enough time on his body and fight clocks to do that.