[jtbigwoo]

Just speculating, but it could be a couple things:

Providing more choices can often result in consumers simply giving up. At a former job we did an A/B test where we showed some visitors two options to buy our product and added a third option for other visitors. In the three option scenario, the bounce rate was about 10% higher.

Or, it could be that there are folks for whom bitcoin is linked with drugs, gambling, piracy, etc. Maybe seeing a bitcoin option makes the site look less reputable.

[VikingCoder]

Well, it may be that using bitcoin right now is... not easy.

"Bitcoin! I've always wanted to try it. [Click.] 'Wallet address', what's that? Okay, I'll just Google Bitcoin. 'Buy viagra and pot online,' oh uhm... Okay, creating a wallet.. Wow, this isn't easy. Okay, now... Time to convert some cash to bitcoins! What the hell?!? Why does it need all of this info? 'For tax purposes bitcoins are not currency,' what the hell?!? Okay, um... What the hell is 'Magic the Gathering'? 'Fraud.' 'Japan.' 'Apologizes.' Hmmm... Ah, forget it."

[digi_owl]

Choice paralysis is something that economists have known about for some time, but seem reluctant to talk about (because more choice has to be better).

[sliverstorm]

To me bitcoin is trendy and kind of unprofessional. Steam is obviously a pretty reputable service, but for a long time accepting bitcoin screamed "this is a low quality service and we have no other ways to differentiate ourselves than using a buzzword currency"