Why should they accept bitcoins? Aside from you just wanting them to, that is. Who is unable to pay them in a currency they accept but who would pay them in pretend internet coins? Do even five of those people exist?
Transaction fees.
They accept prepaid cards, where the merchants have a share of (i don't actually know, so i'm just making a number up) maybe 10%.
They accept credit cards, where the CC company gets a share of 2-4%.
They accept bank transfers, where the bank receives a fixed fee of probably around 10 EUR-cents (for a 10 EUR payment that would be a 1% fee).
If they accepted bitcoins, the fee would be like, uhm, what's the default transaction fee in the client at the moment?
For a company that receives millions of very small payments, transaction fees easily sum up to
millions, they have a strong motivation to lower those fees.