So essentially 80% were not properly registered and paying taxes? I’m not that surprised, once a good double-digit number are cheating, cheating becomes the only viable way to remain competitive.
There is not a big tourist tax here; the biggest tax evasions for private people is probably on their income tax level, but that's not solved by this.
The direct issue it addresses is the take over of many tourists of certain neighborhoods meant for living.
The favorite hobby of habitants of Amsterdam is complaining about tourists.
The fight against Airbnb is a symbolic fight for the left winged parties in the city. Airbnb stands for big bad capitalistic wolf that makes the city unlivable for the normal people.
The issue this bigger fight addresses is that Amsterdam is slowly becoming unaffordable for normal people and especially families. Tourist rentals are partly to blame, but there are many more causes (low interest rate, rich parents, students, limited space and more)
So there are a bunch of restrictive legislations trying to deal with this, this is just one of them. Another one for instance is that since last year it's required to have a permit if you want to live in a house with more then 2 adults.
Already for years it was required to register every night you rented out your appartment. Airbnb however refused to open the books so there was no way to check it for the city. Probably this way Amsterdam can check every registered appartment that's publically listed without the help of Airbnb.