canned sardines...oil vs tomato pack

The typical small can of sardines comes packed many ways......oil,
water, mustard, tomato.....etc.

But those large cans.......probably holding 14-18 ounces......seem to
only come packed in tomato sauce. I've never seen them otherwise.

I wonder why?

Price per ounce on the large can is sooooo much cheaper!! I'd love to
be able to buy a large can of oil-pack sardines, and enjoy the cheaper
per-ounce price.

Lee Carkenord