Why do we have glycogen in the muscles and not glucose? Why do we have glycogen in the muscles and not glucose?

I know this is in contrast to liver cells, which, on demand, readily do break down their stored glycogen into glucose and send it through the blood stream as fuel for other organs. Glycogen is also a suitable storage substance due to its insolubility in water, which means it does not affect the osmotic pressure of a cell.
I think you already answered your own question.  If the glycogen, either in liver or muscle, were all converted to glucose at once it would have a disruptive osmotic effect. But muscles also readily break down glycogen, when they need glucose to contract.  They just don't ship the glucose to other organs the way liver does.