“In total, law enforcement discovered 300 SIM servers – over 100,000 SIM cards – enabling encrypted, anonymous communication and capable of sending 30 million text messages per minute. Officials say the servers were so powerful they could have disabled cell phone towers and launched distributed denial of services attacks with the ability to block emergency communications like EMS and police dispatch.”
you don’t put these SIMs in phones, these go into dedicated devices with very limited functions that pretend to look like phones to operator, dozens per. it can work like a proxy with massive number of outputs
stuff like this https://www.vice.com/en/article/video-ukraine-busts-alleged-russian-bot-farm-using-thousands-of-sim-cards/
also, presumably lots of these cards got burned quite fast, so not all were active at the same time, and some were spares