Oh look, another mmorpg "I know it all"...this is original.
First of all, your premise is highly highly highly faulty. It assumes that there is some universal concept of "easy" and "difficult" with the latter indicating long-term value. Different ppl find different things easy or difficult; it is impossible, therefore, to claim that something is worthwhile only if it is challenging. Nothing could be further from the truth.
As an example, let's take going for a walk. Going for a walk is not particularly hard, unless of course you are obese, out of shape, or have physical limitations. Would you say walking regularly is worthwhile? By your definition, no. But quite frankly, going on walks regularly has remarkable health benefits and many people find it extremely rewarding.
Now before you say, "but learning to walk was challenging," I will counter by saying that learning to do *anything* new is challenging. Still that doesn't make them worthwhile. Learning physics is hard as all get-out, but I imagine a fair amount of ppl would simply say its a waste of time, and many more wouldn't find it fun at all. So please, stop acting like you *know* what fun is. You know what fun is for you, for some, for many, but not for everyone; that is it.
The challenge in any MMORPG is to find a balance. Different ppl have different concepts of "fun" and sometimes the simplest things are the most worthwhile. Learning your first language was easy..you didnt even exert much effort..and look what you can do with it now. You can learn, you can teach, you can joke around with friends...this easy task became very worthwhile. The same goes in an MMO: you need a variety of things with varying difficulties to try and appeal to as many ppl as possible. There's no such thing as one size fits all. Here I thought this was common sense.