I think your numbers are a bit off. I live in Livermore (25 minutes West of Tracy), and it takes me at least 45 mins to drive to SF (if there's no traffic). It's nice that BART comes as far as it does, but it's a 45 minute ride to SF, and that doesn't even include the 15 mins (30-40 from Tracy) drive to get to the station.

I get your point that Tracy has available housing, but I think a 1.5+ hour commute makes it a much less appealing solution than the 50 mins you mentioned.