How many of the OSM mappers work for government agencies? Curious as they should be a reliable data source.

Very few, and in not all countries is government data compatible with OSM's license, so even people employed in state GIS can't necessarily edit the map from the office.

Isn't there a solution to that like dual licensing or restricting free API access for corporations?

It is not that the they make money, but the problem is that corporations with huge budgets can overshadow the volunteer run packaging of the said projects and eventually become the canonical way of using them.

Then the project loses visibility to end users. I don't know if that is worth the occasional commercial contributions from them to satisfy their own requirements.

Why doesn't OSM have a separate price for corporate users of their data? ie: a company with above a certain number of employees pays more

You mean relicensing the project? The data has always been free to anyone. I think you might confuse the map data which is OSM with the external providers whose business is to repackage it into various windows, APIs and other services.