https://www.historyofinformation.com/detail.php?entryid=3496#:~:text=%22Baudot%20invented%20his%20original%20code,and%20Wilhelm%20Weber%20in%201834.

"Baudot's original code was adapted to be sent from a manual keyboard, and no teleprinter equipment was ever constructed that used it in its original form. The code was entered on a keyboard which had just five piano type keys, operated with two fingers of the left hand and three fingers of the right hand. Once the keys had been pressed they were locked down until mechanical contacts in a distributor unit passed over the sector connected to that particular keyboard, when the keyboard was unlocked ready for the next character to be entered, with an audible click (known as the "cadence signal") to warn the operator. Operators had to maintain a steady rhythm, and the usual speed of operation was 30 words per minute."

I think a more plausible explanation is that it's faster to press one key for common letters than multiple keys.

Michael