To give them the benefit of the doubt, you could imagine a situation where they are sending messages that are always PGP encrypted to some process that decrypts

To give them the benefit of the doubt, you could imagine a situation where they are sending messages that are always PGP encrypted to some process that decrypts them automatically. Sometimes they want to send a plain text message, except have the receiving tool still unconditionally "decrypt" it and not, for example, give an error that it is not a PGP message. Maybe it's a bit of a stretch. But it's not too dissimilar to compression formats that have non compressed blocks, e.g. deflate's non compressed blocks or zstandard raw blocks. Their purpose is more for incompressible data or very small data, but can be (mis)used to have uncompressed data that can be "decompressed" by a standard tool the same as any normal compressed data.