8x10" prints happened many years ago when people shot 4x5 & 8x10" film, it was a perfect fit. It was also a great size for magazines and model and actor portfolio shots. 8x12" is the correct size for 35mm but until the later part of the 20th century 35mm wasn't taken seriously and not considered a pro format.
IDK dwayne michaels, HCB, eugene smith and oodles of others ( artists, professionals and
others / photojournalists &c ) did a huge amounts of their work using 35mm. suggesting that
people weren't taken seriously and the format was considered a pro format is kind of out-there.
one could move that thinking to 2017 and suggest that everyone who is a serious photographer
a professional &c uses high end digital cameras ( which they do ) and anyone using 4x5 or 8x10 these
days only does so because they can get the gear at yard sale prices, and they are from the
school of thought that suggests the bigger the negative = the better photographer ... and
shouldn't be taken seriously.