Meat breeds are designed to grow HUGE in 8 weeks. Table sized. That growth rate works great for meat production. But they grow TOO big for their bone density and their hearts. And most either snap a leg or die of a heart attack kept over six months.
Unless you pen them and calorie restrict them - they eat like feathered hogs and all but blow up and burst.
Some tiny few can live long enough to lay but they're obviously not being raised to mate, lay or brood normally and haven't been for thousands of generations, so there are also those problems faced when considering trying to keep one alive beyond butcher date.