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This error is from Boulder, the Let's Encrypt CA software. I suppose that Let's Encrypt staff can say if they have some specific reason to set the limit at ten, the code I read did not offer any reason. But since it's the CA backend, I can tell you that it will not be possible to obtain such a certificate from Let's Encrypt unless they change the software.
Although Let's Encrypt won't issue certificates with more than 10 labels (for whatever reason), you can still get one from aother ACME CA.
ZeroSSL is one that I know will allow more than 10 labels. There's just a little bit of extra work, which is to sign up for a free account (to get your "EAB credentials") and pass some extra flags to Certbot:
One of our software engineers may have a more definitive answer, but: One reason is to avoid excessive DNS queries when traversing a very deep hierarchy to check for CAA records.