I found it weird to realise CPAP machines requires prescriptions some places. In the UK you can just order one next delivery from Amazon.
So patients and doctors fight to have things continue to be restricted so that their workplace insurance will pay for it.
https://www.hope2sleep.co.uk/cpap-machines-sleep-apnoea.html
Amazon is breaking the law by shipping one to you. I suspect there is very little enforcement of this law, which is why Amazon is unknowingly breaking it.
Which law is it you think Amazon would be breaking?
EDIT: In fact the page you linked itself points out that the "prescription" they are talking about is in fact not a prescription. "When the word 'prescription' is used for the purchase or rental of a CPAP machine, this is not like a standard prescription which GP's provide for medication."