Several studies have been done on this subject, and certain themes keep coming up. First is training. Teachers need skills in the language they teach. If they don't have them, they will quit the profession.
There are also teaching skills, because language teaching has evolved a lot. When we adopt that, things go much better.
There's also professional isolation. We teach a subject that no one else teaches. No one understands us. The administrators and colleagues don't understand the material and don't value it. It creates professional and personal isolation, which makes people want to do something else. These are things that we need to invest in and pay attention to in order to change the system and move forward.
As a final point, it's not just language teachers who are struggling; it's teachers, period. We hear that. There are shortages everywhere. However, it may be more acute for language teachers. It's a systemic problem. Again, there are plenty of reports and studies that show this.
It's really going to take serious dialogue and serious thinking to change our education systems. Otherwise, we're going to have teacher shortages for years to come.