guild wars 1 also lacked carrots.
it still kept people playing. for 1 reason: PVP.
if you can't stick to a game for PVP, you won't stick to guild wars.
GW1 offered players instant access to PVP. there were points to grind in PVP too. while your gear and stats were maxed by default, these points could be used to unlock new spells and runes. so if you felt like trying a new build in pvp, you had to grind yourself some points. while similar to WoW's honor system to some degree, it was much more enjoyable in the long run - even with all skills unlocked, there still were hundreds (rather thousands) of new builds that you could try to play, try to optimize... the PvP system of GW was very awesome. even random arena could keep you entertained for months. now add GvG battles and all the other forms of organized group PvP to that and you have a game that can keep players occupied with PvP for years.
If Guild Wars 2 manages to pull off a PvP System that's equal in awesomeness to that of Guild Wars 1 then it will be here to stay.
If it doesn't... well, besides the awesome PvP, Guild Wars 1 was essentially a massive Grind. Players didn't mind back then. Guild Wars PvE had no Challenge or Competition. none at all. From the available Information, GW2 will have similar PvE. bigger of course, more polished, but still not made for competitive gaming or hardcore progression. which means it will get boring quite fast after being played through once.