Because it's not really a useful page to normal users, but it's a funny page to see who has the biggest voting circle or who has invested the most into voting bots, and if anything looks abusive it gets dealt with by the community a bit faster than it otherwise would if there wasn't a trending page. It also must be at least a slight ego boost to those who finally land on it to see themselves up there, and we all know that stroking the ego is a big reason why money is so desired in the first place.
If the SBD wasn't assumed to be 1 USD and it actually displayed the correct ultimate fiat payout amount then we would have perhaps drawn even more (of possibly the wrong kind of) attention these past few months if people were to come in and see the absolutely insane valuations on posts.
I don't disagree about letting people see what they actually want to see and find, I don't think the trending page should be the first page people see, I'm saying that we can have other pages but still leave the biggest hitters trending page somewhere for people who are interested in seeing that kind of stuff.