Blizzard why are you still charging for TBC?

I got a friend to join WoW the other day and I'm shocked to see that TBC is still required to buy in order to get to wotlk and beyond. Honestly, it's a rip off. It's like 100$ to get from vanilla to Cata. Why? There is nothing more from 60-70 now than there is from 30-40 or 40-50. And as a matter of fact 60-70 is the worst leveling from 0-85. I understand buying Wotlk (for atleast a little while) but soon it will be the same and it should be cheaper (at maximum) right now.
I believe once they hit level 11 or w/e it is that they then have to subscribe, they then pay for the latest xpac, which encompasses all content beneath it. No one is asking to get hooked up with everything from 0-wotlk for nothing outside of the monthly 15$.
Blizzard is this going to continue? Buying an xpac is worthless once a new one comes out because the end game is moved to the next xpac. Why should we have to pay for content that for all intents and purposes are gone and are only just a stepping stone. Charging for dead xpacs that are nothing more than just a new zone is ridiculous. Buying the current xpac and then the additional monthly payment is more than sufficient. I hope Blizzard that this isn't because of greed. Regardless, it's disappointing.