I wear a lumbar belt, but dont do it often, because i didnt start wearing one until i hurt my back, so i dont much ride riht now, unfortunately.
Jet skis, quads, lots of sports would benefit from thd safety of a lumbar belt (or a kidney protector that does the same job).
We do a lot of poor lifting form in our sport. Remember, you dont have to be lifting an object to have poor form. We have about 100 pounds above our waist and converting that to foot pounds, it's probably around 200or so on your lumbar just lifting yourself (think you head is 2-3ft away from your waist at about 8 lbs or so, so you head alone just standing up from bend over puts like 30 lbs of pressure on your spine. Compound that with a bent over landing from a few feet up (momentum), you could be loading many hundreds of pounds onto your back.
Also consider people riding stock skis, like my superjet, proper form is hip-shoulder width apart, but the tray is too narrow for hip width (can you sit in it) and you get zero toe turn out. Even with holds on a stock superjet, you may be not wide enouh to push your knees out, so it all goes to the back.