Interesting discussion here, so my few cents:
As was said, in other games the player is rewarded through normal play with xp, gold, items (both yesdrop/nodrop). AO problem is that only xp is the reward. To get credits/items player have to do things commonly named as grind.
For example: new player finish the introduction isle, land on Rubi-ka with few thousands credits (if he even know that there is vendor machine on isle and use it). Then he enter the shop and realize that even basic level 10 implants cost tens of thousands credits. He try to roll a mish for 300 credits reward ... When I started in 2005 as froob, my soldier could buy a yalmaha for 4.5m credits on level 70, not enough credits before! Leveling in SL would be even worse, no credits at all. So for levelling character without credits from highlevel main is farming the only way to have atleast some equipment.
Personally I've got nothing against grind/farm. Problem is that there's almost nothing left in AO worth farming. It's the problem for 220 - most equip is nodrop, everything up to inferno is obsolete, solo play doesn't exist. The only real cash cow on this level is aicity solo farming, but droprate of bots is abyssmal, every other loot is nodrop and/or obsolete and overall it's most boring thing to do in AO. So if you look for reason why so many players got a sec10 twink, here it is (and I know they're obsolete now w/o bounties).