Now, so I don't have to re-type myself everytime, here is a small summary on the main difference in dancing on2:
Again, it is not completely about style but feeling. on1 was really invented in the US mainly because its easier to teach to step on the cowbell for beginners. However, salsa is built on la clave (pa pa pa, pa pa) where your last pa pa hits on your 6-7 counts (or also and-7). So, since your steps are more in-sync with the clave, then they are more in-sync with the music and therefore easier to use the accents and play with the music. Also, listen to a real cha cha cha song. You can only be in-sync in a cha-cha-cha song if you break on2. If you break on1 your cha-cha-cha step is not in-sync with the cha-cha-cha sound in the song. Same thing with salsa - you are only in-sync with salsa when you break on2 (either 6 or 2).
Spin recovery (hang time)
Second, any on2 female will tell you the love on2 better because they know how it differently it feels when it comes to spinning and styling. Because the lady finishes spinning on 6 with her feet apart - she has more time to recover and settle after the spin because 7 is in place and then 8 is the pause. recovering from a spin on1 you don't have this luxury because you finish your spin on 5. While on1 you have 6 to step in place, 7 requires you to put your feet together. Hence, the ladies have one more count to recover from the spins when dancing on2.
Center of Gravity
Now, we all agree that 1,3,5, and 7 are the downbeats in the music (cowbell hits). Those are the major accents. Well, dancing on1, those accents happen in front, in the middle (center) and behind you. Thats because your 1 and your 5. Hence because you are accenting those points, more momentum is generated for those steps when you press your foot on the floor. Dancing on2, your 1 and 5 happen right underneath you, and hence the momentum generated by those steps is neither forward or backward, so your center balance does not move. (or your center of gravity doesn't move for that accent). Because of this, your steps will seem smoother because you reduce the fluctuation or movement of your center. Now, while it might not mean much to the men, it means a whole lot to the lady and how much easier it is for her to spin properly. (especially the prep)
I've already talked about this. You can just count it out. On a prep for a double turn - you both start spinning at the same time. Except on2, you end your spins one count later than on1.
Easier to be smoother
This one is up for grabs as a theory. However, if you look at most of the videos on youtube or from salsa congresses... most of the ones that are on2 are smooth dances. most of the dances that are on1 in those videos aren't as smooth. Why could that be? Could it be because dancing on2 makes it easier to be smooth in your basic step and thats why you have more smooth dancers? Why are there more on1 videos with jerky (LA-bouncing) movements? This is more about statistics than anything else but it helps illustrate a point that there is a difference.
Why you should not dance on2?
Probably cause no one in your area dances it. If you don't care about the above things mentioned. If you don't mind not dancing to the clave. Or you are happy dancing on1.
Why should you?
Well - mainly because of everything above. Also, you should be versatile to be able to dance on any count (but what will happen is the same that happened to me, after you experience both, you'll end up liking on2 better). This way, if a lady loves to dance on2, you can please her (cause remember she'll talk about you to all of her friends). The ladies who like dancing on1 is probably because they don't know/understand how to dance on2 yet. on2 is a different feeling in motion that will let you enjoy the music much more. While on1 and on2 are technically the same steps, they are executed differently - and that makes the big difference.