They don't ask them what they want to pay or what they claim the revenue was, they look at the numbers:

Art. 83(5) GDPR, the fine framework can be up to 20 million euros, or in the case of an undertaking, up to 4 % of their total global turnover of the preceding fiscal year, whichever is higher.

https://gdpr-info.eu/issues/fines-penalties/

Although realistically speaking they're probably just getting fined for one "infringement", despite committing quite a lot.