It's very possible we've not had success breeding them in captivity.

There's a number of species that we've either struggled to, or outright haven't been able to breed.

Squids, for example, were previously thought to be impossible to breed in captivity because they are very difficult to keep alive and healthy in standard aquariums. Once we figured out that we needed HUGE tanks with opaque walls in order to keep them alive, we began to see success in breeding.

They belong to the family Prioninae, which are notoriously difficult to breed, as these insects require very specific conditions that are often hard to replicate in a terrarium.

It would probably have been done by now by hobbyist beetle keepers, if you could just buy them from an online store without any trouble. But they are illegal to buy or own in many countries. You could theoretically travel to the South American forests to find male and female beetles, but the female titan beetles are also really elusive and may take a lot of time and effort to find. Especially since we're rapidly destroying their habitat.