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.