If you look at Stripe’s strategy, they tend to ride certain horses rather throw stuff at the wall to see what sticks, so it wouldn’t have made sense for them to buy 2-3 when they only need to buy 1 that’s really good.
And that’s what they did when the led Paystack’s $8m series A funding 2 years ago when they were almost 3 years old.
Maybe the winners aren't willing to sell early/cheap.
Should Stripe be investing in seed/Round A start-ups? Having Stripe as a resource could be big -- funding, advice, and potentially infrastructure.