With an Anglophone site, you can reach a substantial portion of the internet.
After that, internationalization and localization takes an awful lot of work and resources, for increasingly smaller piece of the internet. Do you focus on rich, internet savy countries like Holland or Belgium? Or, do you focus on the next two largest languages online: Mandarin and Spanish?
And, then, there's always the problem that the US tends to be a bit enthnocentric. And, companies really don't think about expanding overseas until they are relatively large.
Finally, our educational system is very Anglophone centric, and topics like i18n and l8n aren't really covered. I know they weren't for me, and I finished up 3 years ago. So, the learning curve for a lot of developers here in the US is fairly steep, so they tend to ignore the problem.