To start with, If someone has landscaping cloth underneath their patio cover, I'd think it was to prevent sand and debris from sticking to the backside of the top cover.
When they remove the top patio cover to move/relocate, they fold or roll it up without spending a lot of time sweeping the backside before storing it. Once the patio cover is stored, they simply gather, roll or fold the landscaping cloth and deposit it in the dumpster. Remember, they have a whole roll of that stuff.
Don't forget I said, "I'd think".
Me & my Hun RVing for fun!