why would mature follicles fail to release egg

I guess I have been told that a follicle can grow to 22-24 mm and contain an egg but then fail to "release" it. and I was wondering why this happens. or do mature follicles typically release their egg?TIA

I am thinking of <a href="https://glowing.com/glow-fertility-program">ivf</a> but wondering why, after "stimming" and finding "matured" follicles on ultrasound, a trigger is still needed. why not let the body ovulate them and naturally fertilize them. so confusing. thanks