From my reading about this some years ago, I got the impression that they were blaming foreign drug tourists for causing trouble in the Netherlands.
One vivid example from one of these articles that's stuck in my mind was an account of some drunk German tourists vomiting in some Dutch person's flower pot. I've also heard talk of drug tourists falling in to the canals, and some of them have been violent. Of course, many of the violent ones tend to be drunk on alcohol, but I don't hear many calls for Amsterdam's bars to close.
An uptick in crime was also blamed on organized crime being involved in the drug trade, though why the response to that wasn't to just legalize it completely, I don't know.
Mandating that coffeshops be no closer than 250 meters (820 feet) to a school to presumably keep teenagers from using cannabis was also a factor.
Traffic in Dutch cities was up, and that was also blamed on foreign drug tourists.
Blaming foreigners seems to be rather fashionable these days, and the oh-so-tolerant Netherlands is apparently not above doing so itself.
Here are some articles about coffeshop closings: [1], [2], [3], [4]
It's also important to keep in mind that there are the stated reasons for doing something, and then there are the real reasons. In the USA, for instance, the drug war had roots in racism and a backlash against the counterculture and anti-war movement, with which drugs were associated, but the stated reasons for making drugs illegal have to do with health. As has become clear to most people in respect to cannabis, the stated health reasons for making cannabis illegal were complete and utter BS.
I've heard that in recent decades the Netherlands has been ruled by (relatively) conservative Christians, so the real reason might have to do with a Christian moral disapproval of drugs, though of course in a country like the Netherlands which sees itself as very modern, enlightened, tolerant and cosmopolitan such archaic prohibitions could never be stated out in the open.
Another reason I've heard for cracking down on drugs is France supposedly putting pressure on the Netherlands after it joined the EU, and just the pressure to harmonize Netherlands' laws with the rest of Europe. Of course, such pressure has always been there, and the Netherlands has so far resisted to some extent, but maybe their resistance is flagging.
[1] - https://www.dutchamsterdam.nl/548-amsterdam-closing-coffeesh...
[2] - https://cannabisnow.com/closing-time-amsterdams-famous-coffe...
[3] - https://www.telegraph.co.uk/travel/destinations/europe/nethe...
[4] - https://www.economist.com/the-economist-explains/2017/01/10/...