There is an issue around a general teacher shortage, mostly due to poor pay and treatment. It's hard to find teachers in general. It's been exacerbated recently in states like Texas, with proposed book bans and bans on teaching history. No one wants to get punished for assigning Brave New World or teaching about slavery (and teachers don't want to lie to kids about history, either).

Of course, the Trump admin has responded to this by deciding not to fund the TQP grant program, which in part trains and places teachers in high-need areas like STEM, special ed, and bilingual ed. This struggle is mostly a self-inflicted policy choice.