Because of MONEY, a DPS meter while very useful for raiding and progressions guilds to measure and adjust for DPS needs, it does indeed weed out the under-performing players and adds an unwanted pressure to perform / hate & pressure from others which will cause many to quit this game thus causing SE to lose money, it's THAT FUCKING SIMPLE IT'S ALL ABOUT MONEY IN THEIR POCKETS.

There are a lot more bad DPS as to good DPS players, why would SE risk alienating their cash cow?