Because I have a 1 million unique users video streaming service still running python 2.7, using a few servers. The thing has a mobile version serving a different media on the fly, encodes user uploaded videos, features comments, tagging, and even has machine learning detection of content now.
It is still maintained by one single person, and he is not a professional dev.
And I'd say it's already very rare to reach that size in any project, in any company. Hell my last 3 paid projects as a freelancer have less than 20 concurrent users. And that's professional. That's people's real life.
2 out of 3 IT projects fail, no code is even shipped. I would worry about the scaling later. Once you do have the problem, pay the price for more hardware or a rewrite, you made it!
And if you do know for sure you will have the problem (you already work for a GAFAM), then not choosing python is ok, it's not a trap, it's a trade off.
But for the vast majority of us out there, having an easy, solid, battle tested and clean language with a huge ecosystem is worth a 10000 times more than some scaling potential in 5 years down the road.
I have seen so many big C++ or Java project fail I don't associate any language with big and failure anyway. I've seen devs arguing about the purity of this in Haskell, or that in Ocaml, and nothing gets to the end user because it's never perfect, or it's a toy, and doesn't handle IRL.
But what powers most companies ? Rail apps that you won't upgrade ever, but are still running. Spaghetti PHP code and wordpress that just won't dies. Horrible SAP scripts, VBA macros and excel sheets that actually deal with your real data.
Because they shipped. They did the job.