Why does it take a long time to clean the component?
Why are the maintenance costs so high?
The answer can usually be traced to loss of directional control over the blast pattern.
Of course, the blast pattern must be set properly in the first place, but it can change for a variety of reasons.
Wear on the wheel parts which control the "HOTSPOT", i.e. conteol cage, impeller and blades, is the main cause for changes in this pattern.

Inspect them regularly and replace them as soon as excessive wear is detected.