Why do crypto exchanges charge fees?

Could you elaborate on the rationale behind crypto exchanges imposing fees on their users? Surely, the primary motive is to generate revenue, but what are the specific costs or services that these fees cover? Is it simply a matter of covering operational expenses or do they also invest in enhancing the platform's security, functionality, and customer service? Furthermore, are these fees standardized across the industry or do they vary depending on the exchange's specific business model or target market? Clarifying these points would help us understand the rationale behind crypto exchange fees and how they impact the overall user experience.