I decided to edit my question to hopefully make more sense: Going on salary rates alone, why is it more desirable for a company to hire a Java or C# web programmer than a PHP programmer? Their salaries tend to be higher than a PHP programmer, given equal levels of seniority, and it also implies that PHP programmers are less in demand. Granted, there are more PHP developers than in most other web languages, but it's not like C# and Java programmers are rare either.
To be more specific, PHP is not often marketed as a "enterprise" language and I want to know why that is. A lot of companies use it, yet most people don't usually think Fortune 100 when they talk about real-world uses of PHP, just smaller startups and web shops.