Now is the time for really hot take! :ablobcool:
How come PHP is down in the bottom left? It was probably more widespread than Perl and more frequently the "P" in LAMP deployments.
There are more PHP programmers (the dot is red, compared to blue for Perl), so supply-demand balance seems in play.
But what would be the forces driving the sides of that balance? How come they balanced out so differently for Perl compared to PHP?