Tax Day was moved from March 15 to April 15 in 1955.
https://www.irs.gov/newsroom/irs-marks-70th-anniversary-of-april-15-tax-filing-deadline#:~:text=The%20deadline%20was%20moved%20to,and%20process%20increasingly%20complex%20returns.
I know.
They chose April 15.
I’m sure Deep State thought it fitting.