If you want to see a lot of captchas, try browsing with Firefox mobile with ublock origin installed. It's sad how many people design for 100% chrome. To the point that being a stock Firefox user agent that doesn't receive all ads shows up as if you're a bot scraping the site.
It all comes down to how lazy (or perhaps cost-conscious) the developers of the website are. Most traffic is Chrome and Safari, so running those two tests covers nearly 85% of users[0] and most other browsers like Firefox make an effort to fix incompatibilities with Chrome. It’s the same for captchas - most people aren’t running in anonymous mode, and when they are, their IP is usually part of a major ISP and thus reputation can be partially assumed by the IP instead of browser cookie. It often doesn’t make sense to spend extra money just so to appease something like 5-10% of internet users (and might be less than 1% of a company’s actual customer base).
