There is something wrong with the way the latter two render text or place their title or axis labels by default.
Is it the way it is cause MATLAB is a non-free product and more effort has gone into their plot rendering engine? Or is it just the poor defaults of the FOSS options and my subjective familiarity with MATLAB that is tripping me off?
Just see [4] (Matlab) and compare with [5] (Gnuplot) and [6] (Matplotlib). Whenever I plot something with the latter two, the resulting graph appears to be "ad-hoc" and "falling-apart".
[1] https://www.mathworks.com/products/matlab/plot-gallery.html
[2] http://gnuplot.sourceforge.net/demo/
[3] https://matplotlib.org/stable/gallery/index.html
[4] https://raw.githubusercontent.com/JimHokanson/plotBig_Matlab/master/documentation/jim_blog/speed_mac.png
[5] http://gnuplot.sourceforge.net/demo/simple.1.png
[6] https://matplotlib.org/stable/_images/sphx_glr_cohere_001_2_0x.png
One is that the FOSS world is contemptuous towards visual quality, I have gotten sick and tired of complaining about how, in common Linux distributions, the taskbar and "settings" tools are designed with no regard whatsoever for text fitting in the space allocated for the text. There is a real "heads in the sand" attitude about this, they won't accept tickets for it, Linux enthusiasts react violently when you bring it up.
I don't know if I've gotten pickier or if a patent war has resulted in worse algorithms being used but when I started doing a lot of visual design work a year ago I was shocked at how programs like Microsoft Powerpoint and Adobe Illustrator don't properly automatically kern text. The consequence is that if you set headlines in a serif font it looks terrible; go look at a large number of posters people print with these tools and you might think that serif fonts are obsolete, but I think they've fallen out of fashion because they aren't rendered properly so people use sans serif instead.