Is Cruise's Data Network Fragile?

Nearly a dozen autonomous cars created a 15-minute traffic jam in San Francisco last week when the wireless network for Cruise robotaxis failed according to the SF Chronicle:

The autonomous vehicles appeared to be stopped in the middle of Grant Avenue, according to social media posts, with hazard lights on, blocking other cars from moving.

In a response to the incident, Cruise said the backup was caused by “wireless connectivity issues” that immobilized the driverless cars. San Francisco police confirmed that the cell connectivity issues were caused by the large number of people at the nearby Outside Lands music festival overtaxing the system.

It's certainly possible that 75k people attending Outside Lands music festival overloaded wireless networks that the cars rely upon. But, if that's that case it really begs the question: how fragile is the SF cell network?!?

Also, I'm curious why a 3,700 pound autonomous robot driving through city streets with 1,000 pounds of sensors might not have a redundant failover bearer network operating on different frequency bands. Cost?