Well, in Cyrodiil it's like that because of the PvP aspect. You get scaled to level 50 or something like that, so that you don't get 1-hit by a player a couple levels higher than you, or just obliterated by one several levels+ higher. Naturally, higher levels still have the advantage though. It's just a side effect in that the quests there are the same way there.
As for the rest of the zones, it's a sense of progression that a lot of players like. The feeling that you're able to overcome more difficult challenges as you level up. In Skyrim and Oblivion every quest is pretty much scaled to you, so you can effectively pass the main storyline, any storyline really, at like level 5 just as easily as someone at level 50+. It gets kinda boring, because the world around you levels up with you. Feels kinda weird too.
On the other hand it's more accessible and means you don't have to grind around to continue quest series, so it's a balance between the two that they tried to achieve, in that, if you do the quests in one zone you'll be relatively at the right level to continue to the next zone's quests.
A few new PvE Zones will be like Cyrodiil's scaling - in that you're scaled up to be equal to the quest's levels, so you can do them at any time. Orsinium will be like this. So if you like how the scaling system is in Cyrodiil you may enjoy that aspect there.
Also, a few quests in ESO outside of Cyrodiil do scale, like main storyline quests with the prophet, and guild quests.
KrisButtar wrote: »Makes sense I guess. Since I went to pvp and leveled up a good 15 levels, I'm now only doing the greyed out quests that give skill points as that seems to be the only reason to do those select few. Feels like a design flaw or I'm being punished for checking out pvp before I finished pve content. I'm sure i will love Orsinium