I’ve seen a few people who make freeware add-ons that haven’t felt it would be “fair” to charge for said add-ons if they were to be made available to be sold on the Marketplace.
Honestly, I don’t have an issue, at all, with paying for add-ons that are free for PC users. There are $4.99 livery packs on the Marketplace for some of the GA aircraft and that’s really a nominal charge.
I know there are PC folks who feel that free is the way to go, but I’m fine being a part of the mechanism that continues to fund the sim’s development via whatever MS makes from their cut of Marketplace sales.
I’ve also been the kind of person to donate to freeware developers, too, so I’m really not bothered by payment.