I don't think it's due to using non-genuine cartridges.
My view is that it's due to the age of the printer. In its resting position, a printer has it printheads covered by an airtight rubber (or similar) cap to prevent excessive evaporation of ink. With age and use, this seal between the printhead and the cap can fail thus allowing evaporation to take place, this is made worse by the hot environment.
Five years is a very good age for a printer. I think it is time to think about a new one - I don't think a modern one has much chance of lasting five years though!!!