What makes you think gays and (especially) lesbians were mainly backing Sanders in the first place? The New York City precinct data showed that NYC's gayer neighborhoods backed Clinton. It's no surprise that San Francisco would follow. Plus, many gays living in cities like San Francisco are relatively high income, and high income folks generally backed Clinton over Sanders. It's not always all about sexual orientation.
Nonono, you misunderstood me. According to a
poll, half of the users are surprised that Bernie lost that city.
Many, including myself, obviously overestimated the "hippy and hipster vote", while simultaneously underestimating the "gay vote".
San Francisco is well-known for both social groups, thus making it hard to weight their influences on the primary.