AI cannot physically build anything in the real world, what are you referring to? That's a huge part of mechanical engineering.

And you can give it simulation tools, but those are far far away from accounting for everything in real-world physics. You can simulate very tightly constrained problems, but you can't simulate "assemble this actuator and test it", there are so many more variables in the real world that are not easy to account for in a simulation.

If you aren't an engineer that works on physical products, it's hard to articulate just how far from reality CAD and simulations are.