For example, consider that Cloudflare proxies about 10% of the Internet. Well, if you request a site they proxy, and DNS is in the clear, it's obvious who you are connecting to.
But if you request a site and the DNS is encrypted, you could be visiting any one of 10% of the sites out there.
Similarly, if hosting on AWS or Google Cloud platform, there's a LOT of other services hosted in those IP blocks, and IPs change frequently, so there's a significant degree of ambiguity.
This is all in addition to fixing the threat of DNS leakage for VPN/Tor connections.