Then your observation ain't on point. Patial lockdown and cessation of movement has helped spread of the virus countrywide. The numbers of infections you are hearing of are mostly from old Mombasa and Eastleigh.
Well, talking of Kenya as a whole I don't have enough info on how the disease is currently distributed - to be honest. However, I can argue that if the number of new infections is increasing in Mombasa, which is partially locked down, then partial lockdown/curfew doesn't help much at least in that region. The question is whether Kenya is capable of executing 'full lockdown' in Mombasa and other highly affected regions. And if yes, for how long? If the disease gets out of control in the few controlled areas, it's likely to spread like wildfires in other towns of the country.