Other than Dropbox (well, technically they seem to move toward Go/Rust? for core critical infrastructure), I rarely see medium to big scal projects using largely Python. Instagram, while uses Python, is relatively small size shop/group of people. I don't know well how big pinterest/eventbrite.
Some BigCos are using Python for less important projects (scratching their itch maybe?)
I don't mean to disrespect the language or the community, I prefer it over other languages but after reading all Python success story, I concluded that more of them are just for morale booster for the community. 10 years large scale Python project is probably very rare...(maybe YouTube but the again the major use of Youtube is their video/streaming, non-Python)