My sister lives in Palm Springs. Cactus theft is a huge problem, with fat golden barrel cacti being the favorite. A landscaping crew will plant them, and another crew will come along and dig them up and resell them. Similar problems plague construction sites.
A cactus that big would make it easy to implant a tracking device, if police were serious about it.
Where I live it is plumerias - because they grow so slowly and the larger ones are very expensive.
I have several that are small tree sized that were grown 3” cuttings that a friend gathered from a street after several were cut back by city workers (they are now 25 years old). I’ve seen plumerias the size of the ones I have going for $1500. All but one are behind a fence.
Last year, our NextDoor app was full of plumeria thefts - plenty of them. Dug up within minutes and hauled off.
I met a nice elderly couple at the fair last year who told me they had a beautiful large plumeria that was behind a chain link fence - someone came during the night cut it through the fence and then pulled the pieces through the chain links to get it out. It was entirely gone in the morning. They were heartbroken. I had a small one stolen from my school years ago, but none since.
I have a large, beautiful golden barrel cactus that I inherited from someone who retired and left it at our school. It was near dead when I brought it home - it literally came back from the dead and is now healthy and thriving. I was shocked to see one that size go for around $600 at Home Depot. It’s in the back in a pot.