Simplex noise vs Perlin noise

Question

I would like to know why Perlin noise is still so popular today after Simplex came out. Simplex noise was made by Ken Perlin himself and it was suppose to take over his old algo

Answer 1

Some preference for the classic Perlin noise may come from being able to use known values resulting in known visual characteristics, as opposed to investing the time required to find the input parameters needed to get an equivalent output using simplex noise.

[simplex noise] has a slightly different visual character to it, so it’s not always a direct plug-in replacement for classic noise. Applications that depend on the detailed characteristics of classic noise, like the precise feature size, the exact range of values or higher order statistics, might need some modification to look good when using simplex noise instead.
Stefan Gustavson's Simplex noise demystified