It's not like the 8 bit byte was the initial default and others were experiments.
FWIW I believe the 8-bit byte was an IBMism, and for whatever reason I don't remember IBM machines being particularly popular on the ARPANET, which was a research network.
Although its arrival well predated me I do remember a conversation with someone in which we were surprised by how it was becoming common to see people assume that a byte was a fixed 8 bits. I think that was entirely due to the spread of the Vax.
The IBM 360 (1964–) was the killer 8-bit-byte machine.