I don't have infinite time and energy. It would be easier to just not support macOS rather than learn an entire stack just for them. Microsoft also has a Windows-only stack, but its perfectly fine to use others.
I am obviously over-simplifying it, but my point is it really depends on the market you’re aiming for. Like if you think you’ll make an app for users in North America, not supporting Android makes more sense. On the opposite side, if you want India, LATAM, you can drop iOS and never learn anything about Swift since your ROI will be very little. Again, heavily depends on what your goal is.