There is value in being average, in life and in baseball, too. In fact, when it comes to baseball there is a lot of value in it.
Think of it like this. A .500 team in sports is exactly average. You add up the wins and losses for any league, and that's what you have -- a .500 league. That's what we mean when we refer to a sports league as a zero-sum environment. Every point produced is a point given up; a win for one team is a loss for another.
Because of that fundamental aspect of binary competition, it makes sense that in order to put performance in context, we would use average as a baseline. Everything that a player produces that is better than that of an average player should, all things being equal, contribute to winning.
Despite that, the emergent metric of the sabermetric age does not use average as a baseline for comparison. Everyone seems to agree that expressing player performance in terms of wins is the way to go. Wins are, after all, the bottom line. However, we don't usually do so by comparing the wins a player contributes to that of an average player. WAR, whichever version you prefer, does not stand for "wins above average." It stands for "wins above replacement."
There are good reasons for this. Over at Baseball Reference, they've long maintained an explainer for their version of WAR, including a primer on the concept of replacement level. Here's a quote: "When computing the value of a major league player, average is a poor baseline for comparison." The word to zero in on from that snippet is "value."