The IT in question started with Hollerith cards¹, processed by electromechanical equipment. These were originally numeric only — digit n represented by a hole in row n which would stop or start a counter wheel. (Punched cards were processed row by row, not column by column.) The alphabetic extension added a second hole near the top edge, handled using much more complicated and expensive equipment. EBCDIC was originally a straightforward mapping of these holes into an 8 bit space, and its arrangement makes sense seen that way.

ASCII on the other hand derives much more from communications equipment (telegraphy) than IT gear.

¹ https://en.wikipedia.org/wiki/Punched_card#IBM_80-column_for...