Read it again. The low end Country Clipper uses Kawasaki, the low end Exmark uses a Chinese engine, and the low end Bad Boy uses Briggs & Stratton.
Country Clipper also uses Kohler engines. Exmark also uses Kawasaki and Kohler on their higher end models.
When Briggs & Stratton purchased Snapper and most of the box store mower manufacturers the quality mower manufacturers dropped B&S. Bad Boy is a pretty good mower competing with box store prices so for the low end they can not afford not to use the inexpensive B&S engine.
In 2014 I trusted Snapper to put a quality engine on my $700+ 21" self-propelled Ninja (the mulching version). Quite a disappointment. Could not mow my 0.3 acres on one tank of gas (about 70 minutes). The gas cap was in the wake of grass clippings blowing out from under the mower and designed in such a way as to let grass clippings accumulate under the gas cap around the ridge so when the cap was removed the clippings were lifted and dropped into the gas tank. Furthermore it had an "automatic choke" which prevented a hot engine from restarting if left 10 minutes. Had to wait 30 minutes to start, or restart very soon after turning the engine off.
My Country Clipper 18 HP Kawasaki zero-turn mows the lawn in 25 minutes for the same amount of fuel as the Snapper.