Space

It's very different from a shuttle which itself needs to ride a rocket to get into orbit. This is just a reusable stage for a rocket.

It's literally just the US and China that are testing this afaik.

The main reason is for saving costs, as they're meant to be fully reusable heavy lift vehicles (capable of putting over 20 tons into orbit) which is something that doesn't currently exist yet. The space shuttle was the last heavy lift vehicle that attempted partial re-usability, but it still required a massive expendable external tank and booster rockets, which made launch costs still very high. Not to mention the space shuttle was also extremely dangerous, and there was no launch escape system to abort astronauts from a failed launch, and it was statistically also the most dangerous space vehicle to ever fly.

These new things being developed on the other hand, idk what to call them, are supposedly the next evolution in heavy lift vehicles. But seeing as how they too don't seem to have any launch safety systems, and so far have not succeeded a single orbital launch, are still not very convincing solutions.