I would daresay that it's because it's a flat percentage increase in damage across the board. From your auto attacks, from your finishers, from your generators.
As subtlety, your Mastery is pretty good, and is your second best secondary stat. As a massive amount of damage comes from finishers as a Rogue, it's nice to have that high damage boosted. It just happens to come out in the mathematical equations as slightly less important than the across the board damage increase that Versatility has.
Crit is a chance to double the damage any spell or attack does. Crit stacking doesn't work as well nowadays unless you're a Fire mage afaik. There seems to be more diminishing returns on Crit this time around, but that might just be my feeling. This also tends to not work that well on specs that don't have huge damage numbers. As a rogue, you tend to do a lot of fast but weaker auto attacks, you have bleed or poison effects, and all of the smaller numbers that add up to be quite high. Since Crit tends to be a "per hit" and not a "per spell", it can't be relied upon. Imagine if one of your bleeds only crit on 1 of the ticks of damage, rather than the whole bleed effect, quite a massive damage difference.
Haste, well, I believe it's just that as a Rogue, you already attack quite quickly in Subtlety and Assassination spec. So, the main reasons that you would get haste, is to be able to speed up your GCD (Which can only go so low really) and increase your energy regeneration. With the GCD portion, you tend to have to dump a ton of haste into a spec in order to get it to impact this portion enough to fit in that many more spells/attacks for the damage increase to count up high enough, and Rogues are limited by energy regeneration anyways. With energy regeneration, Rogues tend to have quite a few ways of either increasing the amount they are receiving back, or just straight up give themselves more energy, that doing this portion isn't anything to concern yourself about most of the time. If you're going for haste, it generally isn't viable on this spec of Rogue as much because the few attacks/spells you might be able to get in because of the increased energy regen, and the decreased GCD time, won't amount to enough extra damage within the given time compared to the other secondary stats.
As a whole, Blizz wanted to make Vers a better stat, because there were a myriad of posts on reddit and the forums complaining about Versatility being a boring secondary stat, but Blizz responses tended to be "Is it boring just because it's not good enough for anyone? We can always raise the amount of damage it gives you." So, in doing this, and changing up mastery and crit and all the secondary stats, for some classes, vers is now the best secondary stat.
tl;dr Math, math is the answer. There are unique reasons behind each secondary stat as to why the math points it out, but in the end, it boils down to math.