But the API is incredibly expensive. I calculated that I would have spent 3000 EUR the last month, a lot more than the 100 I pay now.

Nothing for large companies though.

I am pretty sure that a hole in the pocket in the order of 50 000 000 USD/month (assuming around 20 000 people using AI in not the smartest or most optimized way possible, therefore burning A LOT of tokens) will be noticeable by even the largest companies.

It is noticeable and even promoted, large companies do pay such sums for the API, like $5k+ per person per month. Not every eng is using AI that much already, but companies are clearly willing to pay those sums.

Per employee?

This not nothing.