This was a much more compelling argument when shared hosting was still cheaper than a VPS with root access. But now you can get a VPS from any slew of providers, like digitalocean, for $5 a month. Root access computing has never been more accessible, and shared hosting is rapidly losing any value proposition it once had. So targeting PHP purely because it's more ubiquitous on shared hosting than Rails, is making less and less sense.
That's still $60 a year, which is at least double the price of a simple reliable shared hosting package. The shared hosting has other conveniences too. I'm not saying it's without downsides, but there are cases for choosing it, and therefore for choosing PHP.
Upload and run with all the security and management done for you is a great way to get going in web development. I don't feel that the idea that everyone doing reasonably simple PHP stuff should have root access 'makes sense' actually does.
