I think the claim might harken back to the days when programming was a new thing and mathematicians,physicists,etc were the ones most often getting started at it, if they had by training gotten used to 1 based indexing in mathematics it was probably a bit of a pain to adapt (and why R and Matlab,etc use 1-based indexing).

Thus, 1 probably wasn't "easier", it just adhered to an existing orthodoxy that "beginners" came from at the time.