I wouldn’t regard Gnuplot as a native solution and cannot understand why Python gets the “last-resort” slot and Gnuplot the “nothing-beats” one. They both are an external dependency and they both need to enter in foreign language territory (the fact that Gnuplot syntax is very shell-like makes just it worse imho).
One reason to pick python over many other alternatives it’s how much matplotlib is used worldwide and consequently how much community attention it gets. Things like xkcd colors (as a sensible improvements over X11) or perceptually uniform default colormaps really make for a greater experience, especially in the numerical computing domain. Browsing the PLplots homepage I just see ugly pure-rgb-on-black figures and awful rainbow colormaps which is really a non starter for me. Similarly with DISLIN.
I well imagine that you can customize as you want in both systems, but having well thought defaults goes a long long way with a plotting library.