Presumably this bill would break the grip that TurboTax has on the market by, say, enabling cheaper and/or free solutions. But using the alternatives would not be in any way simpler than using TurboTax. And TurboTax is not that expensive (<$100 for federal+state).
Of course they'd prefer another Health.gov style spending bill to build another sprawling web service, with the added perk of keeping the friendly government contractors well fed, instead of something that requires the real hard work by the politicians. And simplifying such a complex policy as the tax code would be real hard work.
Instant gratification that can be draws congratulation is always preferred to risking your political reputation attempting to solve the hard underlying problems - especially when they are riddled with special interests as the tax code has become.
Certainly this happens to some engineers, too.