Isn't that the point? To create a rare and exotic spectacle?

The point is to create a spectacle, something that wows the crowd. Exotic wildlife is better for that just by reason of being exotic. But a secondary point is to show the people the awesome power of the Roman state, with its immense continent-spanning logistics capabilities.

Why ship a lion to the zoo when you can fill it with local animals like rats and pigeons?

If scientists are going to clone a woolley mammoth then we may as well go full techno-dystopia and clone some sabretooth tigers to fight too.

Fun fact: Early in their history the UFC turned down a plan to have full contact stick fighting events because they felt that it was too violent.

https://dogbrothers.com/ufc-letter/

Likely not the case, given (1) the body was peri-mortem decapitated (by a human) and (2) apparent structural damage was limited to a single bite mark (on the ilium), with no signs of "taphonomic" damage (indicating limited soft tissue trauma)? [1]

(1) > 6DT19 had been decapitated with a single cut between the second and third cervical vertebrae , delivered from behind.

(2) > Additional [to the decapitation] peri-mortem trauma was present in the form of a series of small depressions on both sides of the pelvis [..]

> Taphonomic damage alone is also unlikely due to the appearance and margins of the lesions, which are the same colour as the surrounding bone (this differs if the break is post-mortem; [56]), and the adherence of bony fragments at the injury site (which occurs when soft tissue is present) .

[1]: https://journals.plos.org/plosone/article?id=10.1371/journal...

If the lion had been mortally wounded by the man, it seems unlikely it would've found the time to gnaw on his bones.

lack of lions

I think you should ask the reverse: What was unique about that time period that created these spectacles?

Entertainment and fighting have always existed (and still do), but usually not to the death.

Christianity. When Emperor Constantine converted Rome to Christianity, he began laying out various restrictions on the games including prohibiting it being used as a punishment or even as an option for criminals, forbade the branding of gladiators, and so forth. Emperor Honorius would then completely ban the games, which had already dwindled by then, in honor of the martyrdom of Saint Telemachus. [1]

[1] - https://en.wikipedia.org/wiki/Saint_Telemachus

The "news" brings you all the death you want, daily. If you want to try it out for yourself there's plenty of Antifa-type organisations to give it a go. If activism isn't your thing you can join a football (the real type, not that silly American game) hooligan tribe for your ritual combat urges. Still not your thing? Join a gang.

Gladiator 'games' were part of the 'panem et circensis' or 'bread and circuses/games' strategy to keep the populace from revolting against the powers that be. They've been replaced by the above, and more. If the silly plebs still seem to be restless there's always another crisis at hand to keep them down, from climate to COVID to whatever comes next.

> what changed in the world that ended these types of death spectacles?

Nothing. Today we have Hollywood and "news" television. 24/7 violence.

Bullfighting is still a thing.