There are PC touch screen laptops where you fold the keyboard back and it becomes a large tablet. Or you rotate the screen and flip it, or pull the screen off and rotate it, etc.. If there was a touch screen MBP that you can flip the keyboard back then you could have something like a portable Surface Studio (or like many other of the PC 2-in-1's). This would be nice especially with Apple's fixation on thinness (even if it would have to get a bit thicker to support the screen).
Besides, as others have stated, Apple does have their keyboard for the iPad Pro. You hold your iPad yet here they introduced a keyboard for it which requires it to be resting on a table, your lap or on the side of the bed. And, because there's no trackpad or mouse support you're forced to touch the screen, whereas with a touch screen laptop, you still have the option to use the trackpad.
Those kind of devices are either solid tables but not very good laptops (eg. Surface Pro), or solid computers but not very good tablets (eg. Surface Book). Those who say Surface Pro meets their computer needs, do not actually need a computer. Those who say their Surface Book meets their tablet needs, do not actually need a table.
I can speak for the latter. 3 hours battery life, for some huge screen, with no optimized apps for touch? I use my table quite a lot to read, underline and take notes in scientific papers. I commute at least two times a week for 5 hours straight in trains, and train stations with no power source nearby. I don't see any advantage in having a all-in-one device.
And this is the reason I own a 9.7 inch iPad and not the big one, and I also do not have a keyboard for it. Apple might sell those devices (and I can see an argument for the 12.x inch iPad for professionals), but that does not mean they're ergonomic. And that's not an excuse to add a touchscreen to the MacBook Pro.