It's a gold sink, only reason why Blizzard stuck it in is for the people who have 10s of millions of gold on their accounts and have nothing to spend it on.
Some ppl are skilled at PVE, others at PVP, and some both. Whether ppl admit it or not, acquiring gold is also a skill and some individuals are quite talented at it. Basically, gold is an opportunity cost. What would you equate 1 hr of time worth in gold? This answer is different for everyone and essentially where ppl differ.
I compare this opportunity cost to that of the RNG chances of a mount drop and the effort involved in assembling a group and running it for weeks/months/years on end to get it. Mimi's Head I use as an example. It's a lot of time invested and often time involves painful wipes until ppl understand the fight. Realizing my capacity to earn gold far outweighs the effort and time of assembling a capped gold char, I was more than prepared to gold cap w/o hesitation if necessary. Luckily, I didn't need to.
Gathering gold isn't a skill, it's a mixture of patience and luck. Patience to farm the materials and luck to get something extremely rare.
It also helps if you use certain AH addons...