Because the egg layer breeds are just that. They do not turn into nice plump birds.
The meat birds tend not to be good egg layers.
If you raise chickens for home use most of us tend to raise what are known as "duel use" breeds. Our Plymouth Rocks will not lay as many eggs as a Leghorn and will not grow as large as a Jersey Giant. They will always fall somewhere in the middle.
For us that is fine. If we were selling eggs for a living it would not be fine.
Got it. Thank you. Sometimes I forget my days on the farm.