There are a lot of reasons people "hate" PHP, or at least look down on it. Some of them are founded, some are not, and some of them are circumstantial.
He mentions seven of the reasons people commonly give for not liking PHP:
- "Inconsistent haystack / needle"
- PHP is a HTML file, with logic
- No standards
- Lack of Quality Packages
- Misconception (about the current PHP features)
- You were doing it wrong
- Elitism ("not using PHP is cool")
There's even more discussion happening on the subject in this reddit post with thoughts from both PHP and non-PHP developers.