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 enforcement of having to separate nomad workers from more shady characters that have exactly the same "signature": long term stays, getting regular money from above, not doing the usual tourist stuff that people that have money and free time enough to stay in a foreign country for months usually do.
So, for law enforcement purposes, it makes sense to have an specific kind of Visa for those "working tourists", so they can pre-filter this population and get back to a smaller working set of persons of interest without the added noise of "working tourists" (digital nomad as a term is incorrect, after all, true nomads would be working locally)