The difference is, if you have an iPhone and want to buy a smartwatch/earbuds you will likely pick Apple made ones, as they are artificially made better than the competition.
While on Android you can pick from a bunch of different companies without any real downsides, and when you want to switch to a different phone (e.g from a Samsung to a Pixel) you won't need to switch your smartwatch or earbuds.
You can use AirPods on Android, but you will lose certain basic features, like software updates, equalizer, changing controls, and more. Not to mention that for a long while you would also be stuck with one different cable to charge this one accessory. It all adds up