There's a missing plane with a bunch of foreign nationals on it and the U.S. needs: (i) a foreign policy win generally, (ii) to demonstrate its alliances and (iii) favor with non-alligned governments/consumers. Further, Ukraine's weaponized dolphins (the obvious, albeit ethically dubious, first choice for this operation) are currently controlled by hostile Russians.
The remaining physical search area (after pingers die) will likely cover thousands of square kilometers of 3mi deep ocean. If the U.S. leads NATO members (e.g., Britain, France, Netherlands and Japan) in deploying submersibles not only would it expedite the physical search, it could also be positive foreign policy press for the administration, demonstrate NATO's cooperation and garner favor with China, etc.
Make some calls.