First of all, I want to clarify that your intention is great, so I do respect that for sure
People on hold their mods on this website don't have us pay for the mods and they do have the option to donate if they want to. It's voluntary praise for whoever that person that is donating thinks deserves the donation.
However, how can we stop people from paying for mods on other websites that are out of our hands?
Besides, let's go beyond the mods... It's not fair that I paid 65 euros for the Steam version of GTA V in January 2015 (Reserve) while others get the game for free as torrent. That is a bigger issue than mods simply because while we can stop people paying (and they don't, anyways) for mods on this website, we cannot stop the huge amount of people that got the game as a torrent and are downloading mods.