It’s not just one thing.
DEMAND is a driver–it’s not unique to the airline industry–look at all of the “supply chain shortages” in almost every industry. There is more demand for nearly every position in the industry. It’s not unique to the airline industry–it is rampant in the GA side of the industry as well.
Couple that with the lack of new pilots (but ESPECIALLY mechanics!) throughout the aviation industry.
From the government side, failure to replace ATC controllers fast enough to even keep up with known attrition times–let alone increasing demand.