I get the rules are rules thing, but I agree with OP here.

Lets say my wife and I each have 200k miles in our separate SM accounts. Now, lets say we want to book a 40k mile award ticket. She has a higher status than me, so it's better for our upgrade odds if we are on the same PNR. So, she books both and spends 80k miles.

Now I have 200k miles and she has 120k miles. Next, we want to book a 140k mile ticket, but we can't! We have enough miles between us, but would have to spend serious money to do the transfer.

It's mildly annoying.