And thats why you can do it your self. Forcing everyone to perform a repetitive task which can be easly automated (for 90% of people) is not a sensible default to take.
According to another post by someone who actually worked tax prep[1], it's more like 30%. In light of that and the delay in the IRS receiving the information from other parties, it does seem like a reasonable default.
The real problem is that the US tax code is horribly, unnecessarily complicated.