This is a CFRG document. CFRG is the cryptographic research community working group within the IRTF. The IRTF does enabling building-block standards work for future standards; they don't publish standards that you, a generalist engineer, are expected to use.

The idea here is simply that the IETF is going to need to do asymmetrically encrypted message exchanges in future standards, and CFRG's job is to make sure there's a well-vetted, carefully designed construction they can pull off the shelf to do that. There is not, in 2024, an existing reference point for this construction that IETF WGs could use, if only because of PQC.

You have to wait for an IETF WG to actually use HPKE before you get to complain about the standards proliferation; it'll be that "customer" (of CFRG) standard that will need to be judged on whether further standardization is a good idea.

It doesn't make much sense to dunk on the actual cryptographers at IRTF, who are more or less just explaining to the IETF WGs how to do cryptography properly.

(I say this as someone who considers themself an opponent of all cryptographic standards bodies).