In May 2018, the Tampa Bay Rays foisted the “opener” on a league that was appalled just long enough it to embrace the idea and save a lot of money in the process. Starting pitchers are both expensive and notoriously unreliable, and lowering the burden on warehousing them was lowered. It was not a small tumble. If you can live with one of five starts being a bullpen affair, why not two? More money saved. The same product over the long haul. Everyone wins.
The same thing happened after the Mookie Betts trade. Owners realized they could trade off their team’s best players before they hit free agency and avoid the fallout by having an assistant hold their phone.