That’s a fair point. Though the inverse is also true. Because the disincentives to quitting multilateral agreements are higher, participants have greater confidence that other parties will live up to their commitments. That increased trust increases their willingness to take risks, giving up something to get something, thereby creating an arrangement with greater potential benefit to all parties.
But you’re right that my argument is premised on the assumption that the United States will not quickly reach comparable bilateral agreements with every TPP member.