That's a fallacy. The benefit of every additional relay diminishes incredibly rapidly. How likely is it that you'll be censored from a rely? 1%? That means being censored from both simultaneously is a .001% chance. At three, you're at a .00001% chance. Choosing 3-5 relays based on incentives is infinitely more effective than sending notes to 500 random relays.

As for increasing reach, that is only the case if a relay 1. allows you to write to it and 2. is used by other parties to execute requests matching your notes. Non-Outbox relays like that exist, (community relays, wot relays, paid relays), but again, in a given context. Randomly broadcasting only increases your reach if you happen to hit a relay you should have been able to select manually (or automatically).

Tldr, you're trying to brute force content distribution. It just doesn't work that way.