They can be. I am making 4x6 bales mostly net wrapped. Some of the people I bale for would rather have 5x6 bales. If they are loading them to be hauled very far they usually prefer the 4 wide bales. If you are custom baling for a cattle operation and all the hay stays on the property, bigger is generally better. Some customers will only take net(most now) last year I offered twine as an option(same price) 1 customer specifically wanted twine and a couple said "whatever". They got net because it was faster on me. I overcame some of the size preference by making very good bales and by making bales that where a full 6' high(no calling them 4x6 and the bale being about 5'6"). I did one field as 4x5's on request. He had a smaller tractor to handle them with.
I have not had the monitor in the tractor or been hooked up since last fall, so the is an guesstimate. Of the over 3000(3500) bales on the counter around 100 are twine wrapped,
Most operators charge less for twine than net. Twine cost's considerably less, but takes about 1 minute more per bale to wrap. I and at least one other area operator charge the same regardless. I figuire the extra time and machinery wear to be worth something.