there's obviously a wealth of knowledge on here about boat electrical systems generally.
But consider the average hirer or, more particularly, a novice. They have a wealth of information to absorb about tides, speed limits, mooring etc etc. If you have a hire yard would you really want to send someone off with coils of cable, instructions about where to buy cards, how to use the posts, where to find them, how to plug in - that's even assuming if they can find one free. How easy is it to set off while forgetting you are plugged in.
From observation it seems to me that the main users of shore power are private/syndicate owners who have the knowledge and can carry the cables and fan heaters and oil filled radiators and all the other paraphernalia and have an in depth knowledge of how to use it.
Don't get me wrong, I'm not knocking hirers (I am one after all)