"Controlled reentry" isn't necessarily synonymous with "booster recovery". Most rockets have a way to deorbit the upper stage once its job is done, either by firing the main engine retrograde, or using a small dedicated deorbit motor. By firing the motor about half an orbit before the projected reentry point, you can control exactly when and where the stage will reenter the atmosphere, hence controlled reentry.
Second, the Long March 5B is somewhat unique among rockets in that its large main stage stays with the payload all the way until orbital insertion. Most other rockets drop a large majority of their bulk long before it has enough energy to stay in orbit for any appreciable amount of time. Probably the closest comparison in this category is the space shuttle's big orange external tank, as it provides fuel for the main engines until just a hair below orbital velocity, but it's subsequently jettisoned and the orbit is completed using the shuttle's onboard thrusters.
So you have a combination of (no deorbit capability) and (big tank floating in orbit) that results in (big tank crashing down at an arbitrary location whenever it feels like coming down to earth).
"Controlled reentry" isn't necessarily synonymous with "booster recovery". Most rockets have a way to deorbit the upper stage once its job is done, either by firing the main engine retrograde, or using a small dedicated deorbit motor. By firing the motor about half an orbit before the projected reentry point, you can control exactly when and where the stage will reenter the atmosphere, hence controlled reentry.
Second, the Long March 5B is somewhat unique among rockets in that its large main stage stays with the payload all the way until orbital insertion. Most other rockets drop a large majority of their bulk long before it has enough energy to stay in orbit for any appreciable amount of time. Probably the closest comparison in this category is the space shuttle's big orange external tank, as it provides fuel for the main engines until just a hair below orbital velocity, but it's subsequently jettisoned and the orbit is completed using the shuttle's onboard thrusters.
So you have a combination of (no deorbit capability) and (big tank floating in orbit) that results in (big tank crashing down at an arbitrary location whenever it feels like coming down to earth).