It comes from trying to use Python apps you found on GitHub before uv tool install was a thing

In the Python ecosystem making software with reproducibility in mind was a thing before the advent of uv. Some earlier options include Pipenv and Poetry. I used Pipenv already some 6y ago to achieve that and later switched to Poetry.

I think devs who didn't care back then also won't care in the future and will still run around with requirements.txt file in 10 years.