I offer GPL source via physical address because I don't want to distribute it with the software and I think the GPL said you have to do it that way. I also provide an email address for convenience but without it being the official way so I don't really have to respond to those. In 10 years, I've had zero requests either way.
It's a 3rd part GPL program that I've modified and distribute with my proprietary software. The not wanting to is just because it's a bit of hassle putting together the files and information on how to compile it in a polished way. If nobody requests it, I can defer that work forever.
