In most countries you can't do any kind of work while in a tourist Visa, but this was never enforced, because it was so exceedingly rare for not to be on governments radar. But once it became more prevalent, it creates the problem (on governments view, especially post 9/11) of having a bunch of foreign folks living for months and receiving money from abroad for god knows which reason. This creates the problem for law…
That's because the laws exist to protect local jobs.
Since nomads aren't 'stealing' local jobs, the laws serve their purpose despite them being broken all the time.
All bets are off if a nomad decided to bar work or waiting at a restaurant! (or any other profession that takes a job from a local).