This is a wild stab in the dark, but it could be some sort of legal distancing or compartmentalization of liability. If this is a pure cost-cutting measure, it hardly seems worth the optics of this action.
Catastrophic failures are a cost of doing business.
... book on an airline that flies Airbus only. There may be a few of those, but it severely limits choice in airline.
... try to determine which Boeing model is used, and be willing to walk away at the gate if the plane is changed out (losing the ticket, or at best incurring a typically large change fee).
For example, American Airlines has tons of both 737 and A320 aircraft, but AA858 seemingly always uses a 737-800 (B738):
https://www.flightradar24.com/data/flights/aa858
* e.g. flightaware.com and flightradar24.com