I'll give you an example of why it keeps the game interesting to grandfather CP.
Our long time, many game, guild leader came up with a harebrained idea for themed PvP. It required me to roll a specific race, with a specific height on a specific class, and I am now required to wear certain armor. It took me a few days to grind to 50 and I am now doing ancillary activities to prepare (get skill points,level certain skill lines, get gear and consumables, etc.).
It's guaranteed to make people laugh and brighten their day, even when we are stomping them into the ground. Even without having everyone ready, people are saying they laugh to hard to fight back. Others on the same faction have joined our tom foolery for short stints.
Completely unfathomable if everyone had to grind CP.
When you have multiple accounts past level 50 it means you can start playing the game immediately after getting to 50 instead of having to spend long hours to get chars useable.