i played coh/cov for a while, good game, comunity is half dead compared to back in the CoH early days though, wich kinda sucks, and sucks big time pvp wise. CoH/CoV got pretty boring for me after having 2 cap lvl characters, and, really nothing to do, waiting for next issues to come out, and finaly got tired out.
for the wow thing, if your longest experience of the game is about 2 hours, you dint get to try much of the content, the game isint really slow paced, but feels like it in the lower lvls, since you dont have any talent builds yet, only a handfull of skills, and such. You dont do instance as often as CoH, thats for sure, since evry mission in CoH was instanced.(but alot of them were the same over and over again wich killed it for me) the instances are more of a big dungeon thing were you go in for phat loot, to make yourself stronger then others. the fun in WoW is really in the endgame, even though most people will tell you <<OMFG WOW ENDGAME IS TEH SUCKS RAID IS LIEK BORING AND ARENA IS LIKE OMFG GEAR DEPENDANT.>> sure, raiding can be boring if you farm the first raid(karazhan) for 30 weeks in a row, if you actualy make progress, and dont bother reading them <<how to>> guides, there alot of fun, and quite the chalenge.
alot of people will argue thta arena is gear dependent, thing they dont realise, thats only in the lower ratings, since that as soon as you break the 1800 ratings, you usualy have enough arena points to have the same arena gear as evry one, making it a fair ground.

now, you asked why more people like WoW over CoH:
WoW is released by blizzard, so its bound to have a large amount of popularity just from there past titles (starcraft, warcraft, diablo
while on the other hand, CoH is made by cryptic studios, wich barely anyone knows(and does no longer exist, mind you) and is released by NCsoft. most NCsoft P2P mmo's dont get much success in the western area(look at autoassault, bloody thing got closed down, and before it did, they were actualy giving copys out at stores like eb games when ever youd purchase something worth 30$ or more, kinda sad)

anyways, this sums up my view of this.