When it's even available. But then they start cranking the ratchet, increasing the no-ad price and introducing a with-ads tier at the old no-ad price, or cutting quality, or cutting corners on customer service and security, etc etc. We've seen this play out many many times and it's a fundamental outcome in even the most basic econ 101 models: an oligopoly with high switching costs is more profitable for suppliers than a free market, made all the moreso by tacit collusion. An unregulated free market is essentially doomed to fail whenever an opportunity to establish such an oligopoly arises.
In extreme cases it does start to look like a protection racket, especially when important services like broadband Internet are involved.