The argument is that support on desktop is so spotty that you are going to have to implement it in JS/HTML anyways. A bare text input field is not sufficient for something like a date or color picker, and is it really better semantically if you have to hide the field entirely if the input sub-type isn't supported?

Then if you are going to implement a custom version, it's easier to just use that on all browsers, since you can style it properly, and you don't have the risk of it changing under you as browsers add support in random version updates.