The difference is how green Mcgregor was when he entered MMA. Khabib was already an extremely high level grappler when he entered MMA. A couple years of boxing training vs Khabib who had 14 years of grappling.
Khabib got into MMA and competitive grappling/sambo at around the same time.
If you're talking about him training from a young age. That's the difference between Russia and the US, vs Ireland. Kids start wrestling from high school (elementary in the case of Dagestan). Most of the bums Conor faced probably couldn't get into college so thought MMA was a good idea.