They are low earth orbit satellites. Generally, the lower the orbit, the faster they decay. You could also argue that this is a benefit in that they gain updated technology with each replacement.

> You could also argue that this is a benefit in that they gain updated technology with each replacement.

No, having the option to replace technology at your leisure would be a benefit. Being forced to replace your technology because it's destined to become aerosolized aluminum in less than five years is a detriment.

Planned obsolescence really only works well if someone else is paying.