Because there are only so many
weeks at #1 to be had, and Roger and Novak soaked up a lot them. One (Roger) before Rafa had even cut his teeth or then reached his prime, gained a lot of weeks at #1, and the other (Novak) rather with no one else to challenge, when Rafa was waning, and more often off with injury. Both had the advantage that Rafa lost so much time to injury. And, even given all that, there AREN'T really that many players ranked ahead of Nadal, in terms of all-time weeks at #1. You say there are "so many." Nadal is ranked #6. Only Connors, Lendl, Sampras, Federer and Djokovic are ahead of him. Not so many, really. And given the time he's had to take off of the tour. Also, given that he's missed more Majors and tournaments than either Novak or Roger. It's not so much of a shortcoming as you (or your emoticon, or your misinformation) imply.
Also, while it gets short shrift around here, Rafa has the
record of consecutive weeks in the Top Ten, and by a lot. 909 to 2nd-ranked Connors with 788. That's a difference of 121 weeks...almost 2 full years. Roger is 3rd, with basically another year behind Connors, (i.e., 3 years behind Rafa,) and Novak is 6th, with 555 consecutive weeks in the Top Ten, which is about 6 and 3/4's years less than Rafa of never dropping out of the Top Ten. Rafa fans have had to endure Federer and Novak fans pressing the "consistency" factor of weeks at #1, and consecutive SF/QFs at Majors and etc., so I will present this one, for consistency points. And, as I mention, it's not even close.