It sounds like a stupid question, but a quick glance back through history, and it isn't as dumb as you think.
Here's a look at the unequivocally best players on championship teams in the past 30 years. I'm leaving off teams that had several good players where it was really difficult to determine who was the best:
PG: Isiah, Magic
SG: Jordan, Kobe, Wade
C: Duncan, Shaq, Hakeem, Moses
First, it's worth noting that there are very few players capable of becoming an unequivocally best player on a championship team, and they account for the vast almost every championship in the past 30 seasons.
The Detroit Pistons in 2004 is the only team without one of these players on it, though several of these players won titles where they weren't unequivocally the best as well [Kobe's 5th ring, was he really better than Gasol? Was Duncan better than Parker in the 4th title? etc..]
Taking a look back at the past 30 years or so, Isiah Thomas represents the only shorter player on the list. The two dominant positions are shooting guard and center. Dirk and Magic (two of the exceptions) have the height to legitimately play a larger position than where they played [same is true of Duncan if you argue him as a PF].
It appears that in the balance between size, speed, and place on the court, typically the shooting guard and center maximize those qualities moreso than other positions [though LeBron is certainly a potential exception at SF].
Most teams have multiple large, athletic wing defenders to throw at an athletic point guard in waves to keep them off their game. There simply exists a fairly large pool of athletic 6'4 to 6'6 guys out there. Such players can keep up with a smaller player in bursts and use their size to defend.
Most teams do not have a couple of 6'7-6'9 guys like that to try and overwhelm a Kobe Bryant or Michael Jordan. At best, their ultra athletic wing defenders are merely the same size, and thus they don't have any true advantage. As such, winning as an elite smaller player is almost always a more difficult task.
Does this mean Derrick Rose can't win a title as the best player on a team? Absolutely not. The Chicago Bulls were not that far off from winning the title last season. The same team would have multiple finals appearances and probably at least one ring if it were together for the previous five to seven seasons in the weak East.
However, the quality of Miami's squad combined with the athleticism of their perimeter players [Wade and LeBron] mean that it will be very challenging for Rose.
It might also be the case that Rose needs a legitimate star to play next to him. Of the above champion's list, the vast majority of those teams were made up of at least two perennial all-stars, and only Hakeem won a title with a second best player worse than the second best player on the Bulls.
Derrick Rose has yet to play a season with a second true all-star even if it could be argued that the overall depth of talent with him is as good as some of those other squads.
Championship teams come together in many ways. I think with the Bulls present talent base combined with the long term assets acquired by management [Charlotte pick, Mirotic] means that the Bulls should have an excellent chance of competing now as well as reloading later.
It may take some internal growth, it may take one final trade, but I think over the next eight years, it does get done, at least once, with Derrick Rose as your NBA Finals MVP.