It has to do with emmissions. Engines today have low tension piston rings for fuel economy and add to that that the rings are- by design- installed in a fashion that favors controlled blow- by.

These factors both work against oil control, so therefore oil usage is increased. The automotive industry was the first to battle this emmission issue. It's now acceptable for an automotive engine to loose 1 quart of oil in 1,000 miles. That kind of usage wasn't heard of 30 years ago.

All this- in the name of progress.....