I'd wager a juice/squeeze issue. Whyte has good wins under his belt since Joshua but he just doesn't have the name recognition. Actually, his name recognition might be on par with Ortiz; but in that case Ortiz provides a tangible upside.
At this point WIlder needs to angle for big fights like Joshua and Ruiz. He's already in his early 30's, the clock is ticking. Granted, those are hard fights to make with DAZN/PBC in the mix, but I don't think it's comparable to Top-Rank/Golden Boy. Both are relatively new and have comparable goals. I'd see them working together just to get a leg up on Top Rank/GB.