Of course, pay isn't the only motivation behind a career choice. Many engineers take jobs in less lucrative verticals like game development because the work interests them.
That said, if you're an experienced engineer and you told me you wanted to make $200k next year, if you're in NYC I would say "go into finance" which is far more limited than the advice I would give in SFBA which is "go work for just about any publicly traded tech company, or slightly more risky go work for a tech company that seems to have an imminent IPO, or more risky still go work for a well-funded private marquee tech company (many of these companies would overlap with the 2nd group). In the end, it's a much bigger pond.
Look, I'm not saying NYC is void of these types of opportunities. I've got friends who work in the city for Tumblr and Spotify among others. I'm just saying, it's about density. You could take the skyline of SF and put it in a few blocks of lower manhattan. And you could take the tech population of NYC and put it in a "few blocks" of SF.
All that said, the relation to wages is more complicated than you suggest. Less variety doesn't speak to the balance between labor talent and demand.