You're correct, they were exclusively paid releases for quite a long time. My personal situation and story is a bit complicated, but suffice to say I continue to struggle financially even now, and this was one of my only sources of income for a couple years. I created these during a time when I was convinced I was going to be making games as a career, but that didn't really pan out.
Aside from the short "Why Diapers, Anyway?" release, and one other SFW creation on a different account, I had never really managed to complete any of my other game pursuits fully to my original vision or satisfaction, and questioned if the value I had been able to provide to people was actually worth the money paid. I know that can be subjective, but the answer I kept coming back to with these was "not really."
And so, after a long while considering things, once I realized I had essentially failed (financially at least) in the game creating endeavors I had imagined for myself, I decided to change the games to be released on a donation basis. This way more people could enjoy them without the paywall barrier, the failure to meet peoples' expectations for their money spent would no longer be an ongoing issue, and anyone who appreciated the creations could still donate if they wished.
I realized it might make others who had already paid for the games feel a little upset, but I understand that position too and am willing to discuss that with folks. I mainly didn't want to keep creating more and more situations like that as time went on. I could have simply deleted the games entirely, but I felt that releasing them to the public freely was a more appealing option overall, even if that came with its own complications.