I've never done much in the PvP side of WoW. I remember doing enough battlegrounds to pick up some gear back in BC, but in general I don't enjoy PvP and tend to avoid it. The reason for this is that I'm a casual player at heart, and PvP gameplay is inherently unfriendly to casuals.
Any game tests the player's ability to overcome certain challenges. If you do so successfully, you win. If not, you lose. And in PvE games, the difficulty of the challenge to be faced is set directly by the game company.
What this means is that the developer of a PvE game can always tune the difficulty to be appropriate for casual players. Of course they may choose not to do so, or they may fail and make the game more difficult than intended, but the option is always there.
In a PvP game, by contrast, the difficulty any player faces is determined by the skill level of their opponents. Since casuals by definition spend less time playing and thinking about the game, they will tend to be weaker players than average. What this means is that PvP as a casual will tend to be a string of constant defeats.
And the game company cannot really prevent this, because they cannot simply make PvP "easier". As long as the potential for a skill disparity exists, casual players are going to be on the losing end.
Now, the usual solution to this problem is a rating system of some sort. If less skilled players are matched with others of around the same skill level, they have the potential to win more frequently. And indeed WoW makes use of this approach.
However, Blizzard has decided that PvP ratings should only apply to organized, "serious" competition - arenas and premade battlegrounds. And this is exactly the sort of content casuals will never participate in! So if casuals want to stay casual, they have two choices - lose constantly, or abandon the PvP game entirely.
Maybe the decision to make ratings only apply to organized matchmaking was a mistake. If normal battlegrounds used a simple hidden rating with no reward potential, the matchmaking experience might be better. On the other hand, anytime you make matchmaking more selective you run into issues with population size. Perhaps the current system is the best we can reasonably hope for.