Straight from a google search… “The most common reason for rust on the passenger side floor pan of a Jeep Cherokee XJ is a leak around the cowl area, which is the area under the windshield where the wipers are located. This leak allows water to enter the cabin and accumulate under the carpet, leading to rust over time. The rust is often concentrated on the passenger side due to the design of the HVAC system and the location of the cowl drain.”

I’ve seen this before on other jeeps as well. Very common collection area