From my perspective, payroll is easy compared to income tax reporting...
There are some, to me, seriously broken parts of payroll, such as the increasing number of tax agencies profiting via required "retirement" or other "helpful" deductions (they contract out the back end processing and keep a cut as profit). The lack of common rules with items affecting all states, such as minimum time in local to trigger nexus. But, there are many families whose living depends on a tax agency having an office to set and monitor rules - process returns etc. - so the likelihood of a tax agency making thing easier is nil.
I saw an article about a non US jurisdiction where the tax agency monitors income and adjusts withholding on the fly so there is no need for tax returns. How would that go over here, let alone across the US? I struggle with this issue whenever I think about it, as simplicity has merit, but will never happen because complication leads to jobs, and opportunity to believe one is paying less tax than required. (I often wonder if there was no opportunity to believe we beat the system, we would not care if the system was made simple.)