It's a cheap way to go with a Chevy tranny like the 700R4, instead of adapting the engine to the trans and then the trans to the D20 you just swap the whole thing in, get a transfer case with the right drop that bolts to the 700 and get new drive shafts. It makes for a simpler tranny swap and motor upgrade.
I agree though I don't like other brand motors in vehicles. I don't even like 350's in Jeeps, there are plenty of good Mopar candidates to put in Mopar vehicles, it just cost a little more money. But I think it's worth the price, to keep the engine in the same brand. I think it caught on and was accepted in jeep's because they have changed hands and did not have v8's until a certain point in time. But now with the new Hemi's, I see no reason to put a Chevy motor is a Jeep.