People often are already able to do that but don't, because surprisingly to some, most people find the idea of leaving everything and everyone you know just to find a better job absolutely dreadful.

We need to remember that we're talking about humans, and not some particle which can simply find a shorter path to wealth.

Edit: To be clear I'm not necessarily opposed to UBI, but I find this 'people are but cogs in the machine' view of economics especially appalling.