One compelling reason is the nature of the US Civil Service. In the vast majority of cases, US government employees are extremely hard to fire or lay off for any reason. As a result, each government agency only keeps a small core of staff that are direct employees and the vast majority of work is done by contractors whose employment can ebb and flow with the whims of congressional funding.
If Oregon had directly hired software engineers they could have built that portal with probably a team of 6 in less time. If we continue making governments have to pay billions for shitty websites, then we'll continue to have to increase taxes and ... big government -> socialism.