There's a theory in linguistics that languages tend to complexify if they're used by a small, insular group, but tend to simplify if they're used as a trade languages. Evidence for this theory can be found in languages like English and Swahili, which are grammatically simpler than their Germanic and Bantu cousin languages. You can also see in Caucasian languages that the languages spoken by higher altitude speakers (who were more protected from the various waves of conquest in the area) being more complex than the lower altitude speakers.
Maybe... Spanish and Portuguese ware used in trade a lot and they don't seem to have simplified much. On the other hand, like English Danish has simplified even further, but it was never a great trade language --it may have been a language of trade in the Baltic basin many centuries ago but not in the last half dozen centuries.
> Spanish and Portuguese ware used in trade a lot and they don't seem to have simplified much.
Latin is another standard example of a language losing complexity due to being learned by large numbers of adults. Greek still has a system of noun cases. Spanish and Portuguese don't.
the relative simplicity of English is pretty much modern, if you go back to the way it was spoken ~200 years ago, I think you'll find it a lot more complicated in terms of expressions and artistic complications, pretty close to French actually
