They have substantial operations in North America. T-Mobile uses primarily their hardware. Nokia still operates Bell Labs which came originally from AT&T via Lucent.
As the other global options for network hardware are Ericsson, Samsung and Huawei, Nokia is the closest to a “Made in USA” solution. Its HQ is in Finland but at least it’s a NATO country now.
So they’re more important to US infrastructure than might appear at first glance.