Why do you refer to The Netherlands as Holland ?
1) because the Dutch do so themselves - only yesterday I drove behind a lorry showing it was from "Kerkrade, Holland"*. Or, if you can tolerate the noise, watch a match by their national teams of football or ice-skating or whatever and note the cries of "Hup Holland"
2) because the English generally seem to like vague postings, some even priding themselves in their ability of working it out just the same.
Holland is a district within The Netherlands
That's perhaps correct historically - I think Holland was a county - "graafschap" at one time - but today there's only the provinces of Zuid-Holland and Noord-Holland.
* Kerkrade being actually in
Limburg - a term even much more profuse than
Holland - but surely Kerkrade is not in Holland (properly spoken) and never has been.