The rationale I've seen is that you're contributing less (risk-adjusted) to the country's economy than either a tourist (who would be spending more) or someone on a work visa (who would have a stable job and be paying local taxes) would.

The belief that DNs necessarily pay less than tourists is largely based on stereotypes. In order to be able to focus on work, DNs tend to look for full apartment rentals, often in relatively upscale places where fast and reliable internet is guaranteed. In many countries that means they are already paying less than ordinary backpackers who are staying in hostel accommodation.

"by definition" always depends on the definition. Tax laws, immigration, I'd say all our reality isn't updated to "people working remotely".

If you detach your job from your (real) environment, this introduces all kinds of issues. You don't pay the share to one of the societies you're embedded into, like taxes. You'd have to be registered as workforce - which you're not, if you're a tourist.

You appear to be subscribing to a weird variant of the lump of labor fallacy here. There's nothing stopping the locals from working remotely for a foreign company -- except a shared language, connections in the field, relevant skills and a proven track record, which are why the nomad is employed by the foreign company and the local is not.