PHP was designed for frontend modeling. He was surprised that people that started using php were using it for backend code as well, which finally pushed the sense of php to where it is now. Noone wanted to use PHP as the modeling language it was designed for because programmers are always lazy as fuck and I guess they were upset serving and manipulating data in C/C++ to serve it to the frontend and finally push it to the user.
I guess that's what i would have done as well. So PHP slowly became rather a data manipulation language than just the output modeling language it was supposed to be.
When PHP jumped from version 5 to version 7, there were huge improvements made as the developers of PHP worked together with some guys from intel to get a better understanding of how data is cached and processed which now leads to a speed improvement of running PHP for up to 100%.
In you wanna know more about php in these day's just take a look at Lerdorfs session where most of my information comes from.