You can casually play PvE. I can login for an hour and do some quests or farm alittle or just chit chat in one of the main towns.
The same really goes for RA, which is why it is the favored beginning arena and arena for PvErs.
How much PvP could the same person do in an hour? Well they could HOPE to have 8 people on to GvG, spend 20-30 minutes probably finally getting everyone to hall and setup, then have time for 1-2 matches max both of which are likely to just be suicide runs against a decent ranked team because of your lack of experience and practice GvGing. For HA you can have 6 people on (soon to be 8 again) or pick up random people and get slaughtered by the Zaishen or spend the time hand picking people and go for 1 run max before having to leave.
GW has long suffered from not being casual enough to appeal to a majority on the PvP side - Unlike the "login and go" of alot of types of games, GW requires large party numbers, setup times, and etc that keeps the average joe blow from competitively fighting.
F

(dont tell my hubby ok?)
but thats just me <a very private person>....