Probably because people who are doing web scraping aren't professional scrapers, they're just programmers who need some data quickly. And since they're already familiar with Selenium, they think that's the state of the art. I've never seen an ad for a scraping service, so I also didn't know that they existed.
That's true when it's a one-time job: pull the data and disappear. I also see how this is the case for most freelancers on Fiverr or Freelancer. This is the tool they know, so they use it. However I imagine there is a number of companies that strongly rely on continous data scraping - let it be for price comparison - and I've seen one heavily using Puppeteer
