Like many things the government "should" do, there is a whole industry that benefits greatly from it not being done. Usually they are the ones who know the most about the preexisting system...intuit, h&r block, and all sorts of related firms would all take huge losses with even somewhat minor reforms (like just sending every wage earner a pre-filled 1040ez with the info the IRS already has).
Same is true for people who support universal healthcare. If you want to do it, you need to decimate the insurance industry. You need to tell a many billion dollar industry to just fuck off if you really want to do it.
Lot of unhappy people out there when their entire career just gets vaporized.