I believe it comes down to mindset.
Vinnie's mindset is nothing is above him or below him, and doing this takes all priority.
For most people, when handed a difficult task, like a piece of complex music, our initial reaction is this is too difficult, impossible, or at least, wow, this is a major challenge. We then need to go to the bathroom, get a drink of water, and suddenly remember something else we need to do. Or just turn it down. The stories about Vinnie is he just sits there and figures it out. He's not intimidated by being handed something he doesn't know. He mentally doesn't freak out.
On the flip side, if a song calls for 1 and 3 on the bass drum, 2 and 4 on the snare, and straight 8ths in the hi-hat, with not a fill anywhere, Vinnie is perfectly happy to do just that. He doesn't ever view anything beneath him, nor does he view himself as too good to do simple work. Most people who are really accomplished or have a high level of skill get bored doing simple stuff, but in interviews, Vinnie will defend simple drum tracks with the same reverence he gives to Zappa like craziness. He mentally doesn't freak out, or get bored.
And there there is the dedication.
I recall on 1990/91, when he got the gig with Sting. He had been scheduled to do a drum clinic at Zildjian Day just outside of San Francisco for months in advance. Then he got the call from Sting. He flew to London to Audition. Then he got on a plane at the last second and flew all the way to San Francisco. I was at the clinic (the store I worked at was a sponsor) and the Zildjian crew were very concerned Vinnie was going to be a no-show. Yet, 45 minutes or so before he was to take the stage, Vinnie walked in, completely jet-lagged. He went on stage and did a mind-blowing clinic. Then he left and went back to the airport and flew all the way back to London to be with Sting. Most people couldn't handle that. Most people would have canceled the appearance in San Francisco. Or asked for an extra day, or at least would have wanted a nap in between. But Vinnie knew he had obligated himself and didn't see the fact he need to fly 8 times zones each way as an obstacle.
And then there are all the other sacrifices. Be it giving up friends, family, social life all to practice. I'm sure the list of typical things we all do that Vinnie has either never done, or doesn't know how to do is pretty long because he's always practicing.