Your number is too low still. Half of those filers are not contributors, they receive refunds. The figure is more like ~65 million taking on this tax burden, so likely closer to 15k (rounding math)
Many projects, many teams. Eventually it all becomes tens of thousands of unread emails, a lot of "thanks, but I've gotta leave for my next meeting", and lots of multitasking.
Your number is too low still. Half of those filers are not contributors, they receive refunds. The figure is more like ~65 million taking on this tax burden, so likely closer to 15k (rounding math)