I think the reason DEXA's are used to diagnose and follow osteoporosis, and not routine X-rays, is to prevent unnecessary radiation exposure. DEXA's result in less radiation. A DEXA scan exposes you to about 0.001 to 0.035 mSv of radiation, while a standard X-ray typically ranges from 0.1 mSv for a chest X-ray to 1.5 mSv for a lumbar spine X-ray.

If you want spine X-rays, you can ask your doctor about it. I requested x-rays when I suddenly woke up with bad lower back pain. I was worried I might have a fracture. The x-rays didn't show any fractures, but verified my severe osteoporosis and also osteoarthritis. I've since read that not all fractures show up on x-rays, but would need an MRI to show them.

Also from what I've read, vertebral compression fractures do not make bones appear denser on DEXA scans.

This article might be helpful: https://www.vintechmagazine.com/x-ray-vs-dexa-scan-unveiling-the-pros-and-cons-of-each/