They can't recruit their way out of it either.
Not enough training bandwidth.
Not enough young people with aptitude, inclination, who can pass a PFT and a whiz quiz. The ones that can do all that aren't dumb... civilian track and a big six seniority number is a very bright shiny object. I was always hell-bent on career military service as a kid, but today even I would have been just bright enough to join the guard instead.
Not to mention they need to retain some mid & senior leadership.