I guess Canonical, who makes 100% of their revenue on support contracts for open source software, doesn't release the snap server code in open source because... what's the reason you are going to come up with? What possible reason is there apart from making it difficult for anyone else to set up any repository at all?
It's the same reason they bet big on Ubuntu on Phones. App stores are worth a ton of money, you contribute effectively nothing and collect 25% of other company's revenue purely because you can lock out any competing app store.
