It's a matter of time. White collar professionals have to worry about being cost-competitive with GPUs; blue collar laborers have to worry about being cost-competitive with servomotors. Those are both hard to keep up with in the long run.
Why on earth would anyone invest in that when you have an infinite amount of human work available?
Have you ever seen the inside of a modern car factory?
> the problems a robot faces when, say laying bricks, are prohibitively complex to solve.
That's what we thought about Go, and all the other things. I'm not saying bricklayers will all be out of work by 2027. But the "prohibitively complex" barrier is not going to prove durable for as long as it used to seem like it would.