Why do touchscreen desktops suck? I'd be happy to touch the reply button below this input form instead of using the touchpad to move the cursor to there and click.
In other cases I'd use the touchpad (the cursor is more fine grained than my finger) but some touchscreen / some touchpad seems fine to me.
Fingerprints on a matte screen? Maybe that's a problem.
The people that have responded to you seem to be focusing on using touchscreen in a desktop-only/work-only environment, but as an owner of a Surface Book I think that's wrong. When I use my Surface Book for work I very rarely touch the touchscreen because, like @fauigerzigerk said, shoulder pain would become a real problem. Instead, when work is over I detach the keyboard, turn the device into a tablet, and switch myself over to "consumer mode". That's when I use the touchscreen; that's when I break out the pen and start drawing; that's when I switch over to using Windows Store apps because they're built for touchscreen; that's when I switch open Edge because it supports touch gestures; etc.
Of course that would assume Apple builds a device that can detach its keyboard or operate as a 2-in-1 where the screen folds over. I agree that as it's designed right now, a Macbook with a touchscreen would be a bad user experience.
This is just an anecdote, but when my last Windows laptop died in October I looked really hard at buying a Macbook and eventually decided I couldn't live without the touchscreen. Pardon the pun, but being able to touch anything on my screen like I can do on a phone just feels right.
(However, I will say that my default work setup [0] is to flip the screen over, place it on my laptop stand and use it as a second monitor - a decent configuration for annotating documents or taking notes with the pen.)
Fingerprints is a problem, but a more minor one. Pulling your hand off the more accurate touchpad is another one. Screen weight/balance is another one, you want a really stiff screen for touching, but not so stiff you can't easily move it.
I'd say one of my biggest peeves is tap area sizes. Your fingers need much bigger areas to tap in accurately, so an efficient touch UI needs way more space for tap areas. But that space is wasted when you are using a mouse/touchpad cursor.
I think Apples stance that the additional costs and impediments aren't worth the minor gains has been reasonable. But it's probably close. I wouldn't be shocked if they changed their minds on their next round of laptops.
This is about making development easier for enterprise developers.