A House of a Different Color?

I live in a Victorian house built in 1900. There are several dozen essentially identical houses in my neighborhood. Call it early urban sprawl, back when the Castro was the suburbs.

So question - why do all the houses have garages? Cars didn't become common until years later. The first Model T rolled off the assembly lines in 1908. San Francisco already had an extensive mass transit network by the turn of the century.

I can't imagine that they were intended as urban "barns" for horses. So what's the deal?