Why aren’t there more successful education startups?

Because the education market, mostly state run, is significantly underfunded and therefore quite careful about how it spends money. It has same basic attributes as social services startups: very fiscally conservative buyers with long lead-time sales, and the business relationship can be cut at any time due to cost or legislative demands.

That translates to a low profit, high cost of sale (due to long resource intensive sales cycles), and volatile post-sale business environment. Each of those is a drag on profits.