That's not how it happens. Unless it's impossible (ex, you target a credit card), you usually starts with Python because, if you know it, that's the easiest option for a POC. Then you look if for this project, it limited you in some way.
When it does, you use another tech. E.G, you needed something to consume less RAM, or you target the browser, or you want an small APK, you need multi-core AND cheap memory sharing, whatever...
But the thing is, short of some very specific constraints, Python is good enough for a lot of things and so we don't "forget" about other languages, we just end up not needing them more often than not.