Because it says:
You will need a permanent mooring with facilities such as fuel, water, sewage disposal, commercial waste disposal, secure customer parking and a safe place to board the vessel. We may allow you to operate one boat using Canal & River Trust facilities, but we will expect you to have access to third party or your own directly managed services if you want to operate two boats or more.
https://canalrivertrust.org.uk/business-and-trade/boating-business/starting-or-expanding-a-boating-business/self-drive-hire
honestly though, I didn't really want the conversation to go down this route, as i said I've seen another thread to do with this and people seem to be against the idea which is fine.
Just doesn't make much sense to me why hire companies buy a boat for like 100k, sell it 10 years later for 40k and have to buy another for 100k. Not sure how much maintenance older boats require compared to new boats which is mainly what I was interested in.