Separate liner vs as cast cyl: more complicated and expensive to manufacture.
I like al engines in some applications, like motorcycles and chainsaws. But where the modest weight differences don't really matter I think fe has more pros than cons.
If my Tempo's cast iron lump was al and saved what- 50 lbs?- that would be a 1.8% reduction in total weight. I might be able to notice the weight loss over the front end with my power steering delete, but if that handling difference was worth the effort I could keep the fe engine, put the batt in the trunk, and end up in about the same place.
My Snapper rider has the al bore B&S and it uses more oil than the Valdez.
Can you hone the cylinder and re-ring? No. Can you bore it? No. Not unless you bore it enough to put a proper iron sleeve in... $$$ while overbore in a fe block + oversize piston is cheap in comparison.
Sure wish that one was fe.