The garages came later. It takes a lot of money to own/care for horses, so they weren't stables, because these weren't homes for the wealthy, just the middle class--the wealthy lived in huge mansions. And who'd want to live above a smelly stable that stinks of horses and road apples? Only the wealthy kept horses at home in town, in separate stables/structures on their property. The middle/working classes took public transportation to work.
They were originally storage rooms or spare rooms. There might be a trend of restoring these San Francisco Victorians to their original "splendor," sans garage.
WSJ
From SF Gate:
Right after the 1906 earthquake.
Circa 1925. No garages here.
SF Gate
Here's the article, "Why San Francisco Victorians didn't originally have garages":
https://www.sfgate.com/local/article...s-16217530.php