Why dont we use potassium hypochlorite for bleach
Potassium hypochlorite can be used as a bleach as an alternative to sodium or calcium hypochlorite. It is not that it is not used but its uses as bleach is not common as compared to sodium or calcium hypochlorite. Enviro Klor™ is a potassium based bleach (12.5% Potassium Hypochlorite Bleach alternative). As written here:


  Enviro Klor™ potassium hypochlorite is a very versatile EPA registered
  (#63838-10, #63838-CA-01) biocide with all the power of a hypochlorite
  bleach and is approved for use wherever typical sodium hypochlorite
  bleach is, including:
  
  
  Recirculating cooling water systems
  Sewage and wastewater treatment
  Disinfection of drinking water
  Public water systems
  Pulp and paper mill process water systems
  Swimming pool water disinfection
  Sanitization of food contact services
  Laundry sanitizers
  Agricultural applications
  
  
  ADVANTAGES
  
  Bleaching and Laundry
  
  
  Allows claims for a more environmentally friendly household bleach
  Provides a sodium-free solution to laundry discharges
  
  
  Industrial &amp; Institutional (I&amp;I)
  
  
  Chemical Compounding – allows creation of sodium free formulas
  Replacement chemical in CIP cleaners
  More stable in certain formulations
  
  
  Agriculture
  
  
  Useful as a disinfectant for wastewater applied to land for    irrigation, conserving water
  Since potassium is one of the three required soil nutrients, there is    little objection to the introduction of potassium ions onto
  land.
  


Here's a table of comparison:



You can see that available $\ce{Cl2}$ (wt %) is more in case of sodium hypochlorite for which sodium hypochlorite is preferred as bleaching agent. Also, byproduct of potassium hypochlorite is potassium chloride for which potassium hypochlorite is used in agricultural purposes where soil needs potassium. Another thing is that potassium hypochlorite may disproportionates to potassium chlorate which is a strong oxidant and may react vigourously with water and ignite or explode.