We've built a total of 18 HHLV's in the past forty years, 13 Saturn V's and 5 Space Shuttles. We realized we couldn't afford to keep throwing away the Saturn V's, so we came up with a re-usable alternative. When you factor in the weight of the Orion (about 60 to 75 thousand pounds) and its cost (at least $500 million per, not counting development costs) and throwing away two-SRB's and four SSME'S per flight (about $300 million for the engines and probably $200 million for the tanks and other equipment), the SLS is almost like trying to operate the Space Shuttle while throwing away the orbiter after each mission.
We spent $18 billion developing the Constellation, and look how often it flew. Will the SLS fly much more often? From the budget, it wouldn't appear so.