It's kind of a trick question since there is no valid reason for doing cleartext DMs but I'm at the same time genuinely interested in why they went with it anyways.
Discussion
I have no idea. Maybe someone more versed in the protocol can answer? nostr:nprofile1qqsqgc0uhmxycvm5gwvn944c7yfxnnxm0nyh8tt62zhrvtd3xkj8fhgpzdmhxue69uhhqatjwpkx2urpvuhx2ue0hswhhl