Probably can't do that easily due to shitty engineering decisions in the past

Or inept managers.

Manager: Why is the site down!?

Engineer: Because it can’t handle this level of traffic. We can rate limit to the level we can handle to keep the service running.

Manager: Okay, let’s do that!

Engineer: Okay. Rate limiting at N req/min.

Manager: I’m getting complaints we’re denying service to customers!? We can’t rate limit our users if they want to use it. Increase the rate limits.

I’ve had this conversation more than once in my career.