Why do companies do this?
I do not have a PayPal account, nor do I want one. But some companies seem to give you no other payment option, do not prewarn you and so you are forced to abort at the last step in the booking/ payment process.
The latest is a holiday club one of my children wants to attend and it really grates on me. I am currently waiting to see whether my ex will use his account to pay and I'll then transfer the money to him. It's annoying.