Per another article : Europol und Eurojust, were able to attribute to the criminal network more than 1 700 individual cyber fraud cases in Austria and 1 500 in Latvia, with a total loss of several million euros. The financial loss in Austria alone amounts to around EUR 4.5 million, as well as EUR 420 000 in Latvia.
So I guess they were providing legitimate business while doing scams at the same time.
After the USA did the exact same thing, I'm predisposed to not trust this statement without seeing any evidence. The USA seems to have assumed criminal activity simply based on the fact of unusual hardware, and I'd like to see evidence the EU hasn't done the same. Perhaps my skepticism is misplaced though, perhaps the police over there are less arrest-hungry and they have only done this after having real evidence that this SIM farm actually belongs to a spam ring and isn't just something they use.
AFAIK network operators are no longer required to know their customer, but may still choose to do so. They're required to cooperate with law enforcement investigations. This doesn't seem like "cooperation" in this case, but rather "police just barge in and take all your stuff" and they probably could win a civil case against the police to get their equipment back or its monetary value, as well as lost revenue. Europe generally has higher rule of law than USA, so there's less chance a judge could say "your business sounds shady so you don't win this case."
The recent EU-wide Digital Services Act has generous liability protections for "mere conduits". A mere conduit is anyone who is just getting traffic from A to B, unless they are A or B themselves. Even though in this case their cellphone operator may think they are originators of traffic, if they are a relay business (and not spammers themselves) then they are mere conduits and protected from liability*. Of course they must still cooperate with law enforcement to track down the source of the spam, but they are not required to pre-emptively KYC. Having their office raided and all their equipment stolen doesn't sound like "cooperating" to me.
* their cellphone company probably has the right to terminate these SIM contracts, and may also sue for damages, but I suspect the damages would be something like the difference between their actual cost of SIM cards and the EU-prescribed maximum wholesale rate for sending texts, which is likely a negative number.
So I guess they were providing legitimate business while doing scams at the same time.