Not sure I understand your offerings. You seem to suggest that you offer code signing without an Apple Developer subscription? So are you using your own certificates to sign your clients’ code? If that’s the case it sounds like you’re probably breaking TOS and opening up your clients to immense risk: one client’s abuse results in all clients’ apps revoked.
Unless free actually means a cash allowance (which would be very generous), I don’t see how this would work. I’m certainly not gonna let someone else register and pay for an Apple Developer account on my behalf.
This is just one of my guess here. If you look at the commit history the project doesn't look like being the main focus. Code signing is not as streamlined as Let's encrypt, the money part makes it bumpy, so I'm not surprised.
