The place where DoH is common is the place with no network effect. Anyone can use anything from DoH to DNSCurve to OpenVPN to secure the path between the client and the recursive DNS server, and can do so regardless of what anybody else uses for that.

The thing we're still missing is something to secure the path between the recursive and authoritative nameservers, which is the thing DNSCurve is actually better at and is also not the thing DoH is commonly used for. Moreover, "adoption" is basically code in this context. You could have widespread adoption of DNSCurve just by adding support for it to the handful of open source DNS servers in widespread use.