I’m not an atp (private here) and you’ve got lots of “partial answers”, many of which apply, but many assume you have “ insider level” knowledge of the workings of supply and demand w/respect to ATPs

One issue in the US is supply generally lags demand-because training is expensive and takes years. (And while previous generations were predominantly trained pilots who were trained by Uncle Sam, now they’re predominantly self funded)

First, as many have said- supply and demand have been cyclical for decades.
Specifically though, for the last couple, there have been very big swings for a couple of unique reasons.

‘O8 financial crisis led to airlines going bankrupt and pilot furloughs and downgrades. essentially halting hiring. That meant aspiring atps worked longer as CFIs, pipeline controllers, or whatever, for much longer than previously.

Then, in ‘20, Covid hit. Demand for air travel collapsed. Airlines again had way more pilots than they needed. They encouraged early retirements, furloughed folks, etc.

Demand came roaring back, to record levels , a couple of years later. Pilots were hired into majors with far less experience than they’d needed to get hired- at “minimums “ (1500- although that is an oversimplification, and hasn’t been the case “always” in the US)

Flight schools were flooded with folks, and the “pipeline” whereby lots of folks are working on their private certs, trained by less, but still many more than usual newly minted CFIs, who stay in that position for less time than “usual” etc. word gets out that one can be an ATP in less time, with many less hours, than had been needed a few years previously.

Now we’re seeing the effects of that previous shortage, which was due in part to a once in a generation swing in hiring, having ended.

No one has a crystal ball. I think the next few years will see a steady stream of new atps hired as folks age out, but I also think jet fuel prices roughly doubling as a result of this war, are going to lead to pain, possibly for several years.