Microsoft makes $70 billion per year from Azure, and 40% of Azure servers are on Linux. That seems to imply $30 billion come from Linux hosting. And these are the guys who make Windows. When your rival makes 30/200ths of their total yearly revenue just hosting YOUR servers for people, I'd say you're not going anywhere any time soon.
And that's just two companies. When the revenue generated by services built on top of GNU's projects dip below $1 billion worldwide, I'll lend an ear to someone telling me they are dying.
But using money as a proxy for activity, $40 billion dollars (at the very least, and across only two companies) all say GNU is bustling.