It seems to be a pretty clear case of "failure by success". Python, JS, and PHP were so good for developing applications that many people wrote huge ones in them -- including companies that made billions of dollars like Google, Facebook, and Instagram. GMail and Google Maps broke new ground in terms of JavaScript applications (using the Closure compiler, which is probably almost 15 years old now.)
At the start, those languages tended to be used for 100-line, 1000-line projects. They work really well in those domains. 5K lines works fine for single person projects too.
Once you get to 10K- and 100K- line projects, and you have 10+ people on a project, types start to make sense. You can't change 10K lines of code at once, so you might as well have some rigidity.
Also note that you can do a lot more in 10K lines of Python than 10K lines of Java, C or C++ -- and in the 90's, when those languages came up, those were basically your choices.
At the start, those languages tended to be used for 100-line, 1000-line projects. They work really well in those domains. 5K lines works fine for single person projects too.
Once you get to 10K- and 100K- line projects, and you have 10+ people on a project, types start to make sense. You can't change 10K lines of code at once, so you might as well have some rigidity.
Also note that you can do a lot more in 10K lines of Python than 10K lines of Java, C or C++ -- and in the 90's, when those languages came up, those were basically your choices.