Being Elite in one program (say DL, like me) got you points in the same program (DL) when you used the other guy (SPG). That encourages me to stay in SPG when I might not otherwise have done so. I would assume I'm the target - Marriott faithful lured to get some extra points by switching to some SPG.

In fact, I did. And made SPG Gold. So it worked on me (a little). I say a little because I didn't like SPG that much and will probably let the Gold run out. Meanwhile though I will get free SPG points for my Delta $$ on the vice versa of the example above.

The fact you are lifetime Gold is what makes it not make business sense in your case. Can't be too common though.