It's not a port when the tools to compile for Android are directly integrated into the development platform.
Also, as I understand, it requires a certain understanding of the development process on Unity to actually successfully save an Android compatible version. And then it should be fairly straightforward.
Maybe the dev never actually planned to release on Android?
BTW, it is more difficult to build a Mac version on Unity than an Android version due to the odd ways Macs work.
Thing is, it's not so much to do with what's easier or not than what the devs know how to do. It doesn't matter if compiling a Mac version is easier if the dev understands that but now how to make an Android version. It'll still be hard for them to make the second one anyway, in that case.
People tend to assume devs know how to make anything and they just have to ask, but 90% of the people who start making a little game project like that actually have little experience in some part of the process and learn on the fly, either because it's necessary since they don't have someone to do it, or because they want to learn it and making an actual game is better motivation for it than just reading a bunch of tutorials.
Has to be better than all those renpy-mockup-emulation-sort-of-experiments going on.
Weeeeeell... The thing is, Unity is an engine that can do a bunch of stuff, while Renpy was specifically made for Visual Novel games. It doesn't really compare... It's like trying to compare how a baker and a pastry chef can make a wedding cake. Sure the first one works with food as well but it's not specifically his ballpark to begin with.
Renpy was created for that specific type of game, so the tolls are cattered for it, which helps the process by not letting the devs waste time creating the setup for a VN-type game, and not letting them wander too far from the formula. Unity is more general, you can do multiple types of game, meaning you have to learn how to make the specific framework for the type of game you want to do.
In a way, it's more work, and it also means it delays the development process.