Online credit card payment systems and other electronic payment methods (not including bank transfers) are so open to fraud its not funny.  Keep in mind a credit card chargeback can occur 60 to 90 days after the transaction has taken place.
Unless the vendor physically has the card in their possession, swipes it and visually inspects the signature (unless is a pin) at point of sale, you expose yourself to potential fraud.

Then on top of that you add the paypal fees, or merchant fees on each and every transaction.

Now for a proper e-commerce site like Marco Spec - you'd be looking around $60,000+ to get it setup, all inventory listed, photos, prices, shipping modules etc and its a tonne of work.  You'd need to employ a full time person just to keep it running, up to date and secure.  That would equate to around $50,000+ per year in salary alone.

We've all seen the free e-commerce sites which are clunky, impossible search engines and terrible layout.  Others try to use Facebook etc....

Yes PBR are not using up to date payment methods.  Would it be easier for the customer, yep.  But I've ordered from them probably around 20 times and is not that hard.

They have been in business a long time and have been quite successful.  Once online transactions become bullet proof they may look at it.  I have no doubt they've looked at it, made a risk assessment and simply chose not to.