I'm not trying to play down his side of things, he couldn't really have done much more, just pointing out that it absolutely takes two to tango, and without the UFC machine behind him he wouldn't have anywhere near the same reach. My point being that I think too many people ignore that when talking about how other fighters should promote themselves better. Sonnen worked harder to promote himself than anyone and he was quite a genius at it, there was also less fighters around at that time and public interest in MMA was hitting new heights, but he still didn't get close to McGregor levels because his background just didn't have the same advantages in terms of demographic. That Irish, but particularly, Irish-American market was just begging to be tapped into when McGregor arrived on the scene. As a result they were fully behind him from the get go, cutting promos after one fight against a no name bantamweight, then after his second fight (UD against Holloway) they dedicated a whole fight pass documentary series to him, as well as huge promotion and build up for the comeback fight, headlining in Dublin against Brandao. Headlining a show after a win against a bloated bantamweight and a decision against a 22 year old kid who people still didn't know at that time. That doesn't happen without a serious marketing angle and push.
Diaz had just enough of a cult following in MMA to get the call to be a late replacement for 196, he wasn't really doing anything different to promote himself than what had him on a 12k+12k contract. Just had a good performance against Michael Johnson, called him out somewhat hopefully as McGregor had already been booked to fight RDA and then due to injury and timing he got the call at the last minute. Then we saw what the UFC marketing machine can do once it gets behind you. After the win all of a sudden Diaz went from being a lightweight gatekeeper on a 12k to show contract, to being a huge welterweight (apparently) and one of the pound for pound top fighters. Now he's probably only behind Conor and Ronda in terms of popularity.
If you look at a guy like Tony Ferguson, he's kinda similar to Mcgregor in many ways. He is an exciting fighter, who is unashamedly cocky, even does the wearing shades indoors shtick and says similarly outlandish stuff in interviews and press conferences, but never once received a lick of promotion from the UFC. Now he's 11-1 in the UFC and on an 8 fight win streak and just got passed over along with others for the title shot because the average Joe still hasn't ever heard of him. That's largely due to receiving no backing from the UFC, which in turn is largely due to not really having a good demographic to tap into. For your shit talk to get you places you need to have a loyal fanbase to soak it all up and help it grow. Otherwise you're just left looking like an arsehole pretty much.
You heard Mendes after his fight against McGregor, he was in awe of the Irish support and said he wished that Americans could get behind their athletes in the same way. But it's too big a country, with too many fighters and sports people in general to get support purely for nationalistic reasons. It's not really a matter of general American national pride, they can take pride in having many great athletes rather than one great hope. That's why American fighters are very often promoted as something other than American. Cain and Mexico being a perfect example, he couldn't even speak Spanish when they were trying to bill him as the great Mexican hope in MMA. Stipe has the loyal Cleveland following which is a good angle for him as we all saw the amazing support he got at UFC 203. However he had to get the belt before reaping those rewards, he wasn't receiving any love beforehand.
Ronda was/is all about girl power and being an olympian, which combined with some amazing to watch performances where she'd finish girls in seconds, particularly the fairytale submission of Cat Zingano in her first PPV headliner, to really skyrocket her. What is clear in both Ronda and Conor's case is that conditions had to be right in many areas to make them such stars and that includes a number of factors outside of their control and usually a 'hollywood' moment or two that was hugely unlikely to happen. The Cat Zingano submission was pretty much a freak occurrence in the same way the Aldo flash KO was. You are right that McGregor had already become a star before that but I think it's fair to say that moment and winning the belt catapulted him even further.
Once again I'm not trying to blame or take away from Conor. He absolutely worked hard to promote himself and then performed amazingly in the cage to back it up, but it's just interesting to look at how it all comes together. I mean we've seen how the UFC have tried to do the same with Sage Northcutt, look at the crazy push he was getting, but he wasn't ready for it and couldn't back it up. 99% of fighters aren't getting that McGregor/Rousey/Northcutt push. McGregor and Rousey managing to run so far with it is all credit to them.
Love it.