Why would I pay £5 p/mb when I can pay the same £5 for an hours access and consume as much data as I like during that hour? Paying £5 for an hours access is massively over the odds but £5 p/mb to skip the few seconds of "inconvenience" of having to register* for a service... err, yeah, no thanks.
*Lufthansa only want your email address and a password if you pay via PayPal, their access points web app works with the PayPal app (if you have it on your phone) so you don't even have to bother digging out your credit/debit card.