1. The time scales are completely different for internet and biotech. A/B testing online can take hours or days while biotech experiments take months to years. In fact, I came up the idea for the startup while I was waiting 4 months for a substrate to be synthesized!
2. The costs are also dramatically different. The limiting reactant isn't people, it's $$$. Biotech is extremely capital intensive. Equipment, reagents and people all require significant amounts of money over a long period of time.
3. Lastly, hard sciences do not have a monopoly on "big problems". Maximizing my impact is a desire I share with many of the HN crowd. For me, the impact I foresee by improving rating systems dwarfs what I thought I could accomplish in bio-nano. Don't get me wrong, this was simply the right decision for me, which is why I dropped out a year ago with zero regrets.