In today's mobile-connected society it's the work of less than 30 seconds to fire off a text message to a seller asking for all sorts of photos. No real effort required therefore much easier for tyre-kickers. From a seller's perspective they might have three or four requests for extra photos, so they have to got to the boat, take specific pics and send them on to some random on the internet that they then never hear from again. All that effort for nothing. I had this when selling cars in the past.
Serious buyers pick up the phone in my experience. It shows the seller that you're not just a tyre-kicker and therefore it's likely worth their while to send extra photos.