Turning off Wifi is not something anyone - whether average or intermediate user - should be needing to do on a frequent basis. Airplane mode already takes care of the primary use case, namely disabling all radios. Someone intending to disable Wifi "temporarily" and then forgetting to re-enable it may wind up paying hundreds of dollars for cellular data. That goes against the "it just works" mentality, which is "Wifi automatically wherever possible. ALWAYS. Cellular as last resort only."

Privacy is less of a concern on iOS; the MAC address is rotated frequently specifically to prevent passive tracking. The battery savings are going to be minimal; with Apple's history with these kinds of optimizations, you'd probably save as much battery by reducing screen brightness by only 5%.

tldr; There's no real reason outside of developer testing to ever disable Wifi. Users who care should not mind the extra tap. And frankly, most who are obsessively toggling their Wifi are probably not receiving the benefits they believe.