Some people probably switch to using the API, but no-one has ever contacted us. They either give up, or run their scraper on a different computer -- I've seen the same scraper move between university computers, departments, then (in the evening) to a consumer broadband IP.
If pages are driven via an API, then the API is preferable, but publicly facing websites are often a mix of server-side HTML generation and API enrichment, for caching if nothing else.
My client is under no obligation to make access to this data easier. It's not really their data either; the information is property addesses, owner names and addresses, and tax assessments and payments. My client wouldn't want to make it easier for scammers to get that data. So they're not going to do anything unless they know the scraper is legit. If that's the case, the api would require authentication, and any fees would be for the server load, not the data.
Some people just don't care for the commons
The ideal answer and the efficient answer are not usually the same.