Why do so many European and UK based SaaS companies charge in USD only?

I've always generally been a person why tries to support a startup or company from the United Kingdom or the European Union as opposed to one from the United States. I already feel the global internet at large is far too Americanised.  All the major players on the internet are US companies, and this includes most of the well known startups too.

Perhaps the largest consumer of Internet services are American companies and citizens; as it definetly seems that non-US companies cater for the US audience and economy in preference to their local one.

Now it's true that whatever currency a company happen to deal with, the effects will only be felt locally to them, i.e. it would become a great importer, I'm still puzzled as to why non-US companies still deal with US Dollars instead of their own local currency.  I've yet to see options where the company will accept both US Dollar and their own local currency.

Even the largest internet companies such as Apple Developer Registration, to Google Apps, or Microsofts Azure deal with multiple currencies in addition to the US Dollar (Amazon AWS meanwhile is still a notable exeception billing in dollar only).  So if these large companies do it, then why not the new wave of startups?

With the vast range of payment providers, from Stripe,  Braintree, GoCardless and Paymill; there's certainly no technical excuse I can think of to restricting the sales currency.  Surly doing so, dealing with a non-local currency, must incur them a sizeable sum spent in foreign currency exchange transaction fees year-on-year, let alone exposing themselves to the fluctuation in foreign exchange.

I asked UK based domain registration company DomainBox why they only offered billing in USD as opposed to the pound.  They said it was because that most of the revenue they collect is then passed on to each domains registrar to settle the charges they levy, and since they all also charge in USD, it's more financially effiecient for the to maintain funds in the same currency they pay their onward supplies.  In contrast to this, French company Gandi (who also are domain registration providers) charge their customers in Euros - despite having to settle with the same underlying domain registrars in USD as DomainBox do.

Do you work for a non-US company but still bill in the dollar, if so why? Follow up in the comments.