A co worker use to own a small sewing factory that contracted sewing some clothes dept stores. He did all the sewing machine repairs. He said if the machines had outside threading lint wasn't a big concern, just clean when you see the lint. It's the inside threading the new machines have that lint build up will cause damage. You can't see or get to the lint in them. Vintage machines have outside threading with lots of thread guides. Thread guides are very useful for a good stitch. It's cheaper to make a machine with inside treading and horizontal spool spindles and few thread guides. The savings can go into other features of the machines that most want these days.