But you're working abroad for a company that's treating you as if you are living in your own country and is, presumably, depositing your paycheck into a bank in that country. The fact that I'm traveling somewhere (on business or pleasure) during a given month basically doesn't affect anything. I travel maybe 100 days a year, in part outside the US. I don't consider myself a digital nomad but the reality is that I'm outside my home country for a decent chunk of the year.
There is a limited range of activities permitted on those, including attending meetings and conferences.
But mostly, US and EU citizens in particular have visa waivers or, at most, a visa on arrival that lets them do normal business travel things. They just can't take a local job.
To the upthread comment, neither myself nor anyone I know has ever been aware of any particular tax implications associated with ordinary business travel.
It can affect your taxes dramatically. Bump that up to 335 days / year outside the US, and you're entitled to the foreign earned income deduction, which last I checked was about $120,000.
That's not evading, though; it's a formal deduction.
1. Sovereign countries are permitted to care about whatever they want, for whatever reason they want. They can enact any laws they wish, protect their border however they wish, and grant anyone the right to work in their country based on whatever reason they may have. When a country is not granted the right to permit (or not permit) someone from entering/working, they lose a part of their sovereignty.
2. How would a country enforce its own tax laws without a formal entry/authorization process?
3. How would a country enforce international tax treaties without a formal entry/authorization process?
4. Working abroad, without any kind of work visa, would make it incredibly easy to evade paying taxes in your own country.