It's a market segmentation thing. Hotels that cater to business travelers can charge extra because the employer will pay for it. Hotels that cater to families usually have free internet.
> Hotels that cater to business travelers can charge extra because the employer will pay for it.
More likely, IMO, hotels that cater to businesses have separate charges for internet because business (especially government) travel offices often have fixed (sometimes location-sensitive) caps on reimbursable lodging rates (but may, or may not, separately reimburse for other services during the stay with appropriate justification), so pulling non-core services out of the core rate means that more travellers will stay there.
Families, conversely—while price sensitive—will compare amenities and rarely have strict caps for the base lodging rate irrespective of what other services are included.
>"It's a market segmentation thing. Hotels that cater to business travelers can charge extra because the employer will pay for it."
What does this actually mean any more though to "cater to business travelers"? Once upon a time a hotel that catered to business travelers had a "business center" which meant there was an auxiliary room with a fax machine, a photo copier and a couple of PCs", that is largely anachronistic now though. And I think this kind of illustrates how stuck in a different era most of these hotels are.
Another response below correctly answers your question. In business hotels, rates are set to be eligible for corporate booking. Expensing the internet separately is a non-issue for these customers.
