There are a lot of people who interview at the big tech companies + a couple small impact oriented startups, but it's very rare for them to take the small impact oriented startups offer. It's hard to turn down 250k a year.
I actually don't think this is true. Many computer science students are not only looking for morality in companies but also excitement. Also it's not 250K. Big Tech might give advantage of like +15K. Also, the work is not nearly as exciting. It's safe and cushy, but as a person in their 20s out of college, safe and cushy isn't fun.
As a new grad out of college with friends at FB, I can attest that it can actually be 250k (base + equity + returning intern signing bonus). At least for year 1.
15k? Maybe it widens as you gain experience, but my last job search (at ~3.5 years of experience) resulted in a 90k difference between the highest startup offer and lowest non-startup offer.