It's a very useful service, and there are some strong arguments why it should be free, but getting people to actually adopt a standard is really hard. It takes a lot of effort, time and money. Without the possibility of revenue it's very likely no one would ever have funded it, so it would never have happened.

It'd have been nice if W3W was the product of a foundation like Mozilla, but it's not. There's no reason to begrudge the founders wanting to turn it in to a business.