There's not a lot of evidence that full body MRIs are beneficial. A lot of people have pre-cancerous growths that may or may not become cancer in the future, so you may just be giving them unnecessary surgery, and surgeries are not risk-free. If you don't operate, they might develop an anxiety disorder.
We do a lot of CT imaging in the emergency department and it sucks if we incidentally find an abnormal growth in a young patient's CT head. These are usually benign and often not worth performing brain surgery to get a biopsy.
Why not just rescan them every few months to see if it's still growing? After all, you wouldn't have to rescan the full body, just the section where the growth is.
I had one at detected at 5mm close to the amigdala and they just scanned again in 3-6 months on MRI to prove it wasn't growing. That was a decade ago.