The point is to have a DMARC record, setting it to none doesn't really do much of anything for you though. If you really wanted to take advantage of it you will need a DMARC monitoring solution - the market seems to typically price these around $10/month for small-ish domains (though there are a lot of caveats). I'm trying to build a reasonable free option that maybe isn't enough to get a domain to a reject policy, but should be enough for you to maintain a reject policy.

The truth is that there are amply "non-sending" domains out there which ignore DMARC and allow abuse. Stopping the assumption of no policy mean p=none prevents this abuse from persisting.