User blog comment:SkyAzurePhoenix/Irregular List/@comment-34544409-20180507120422/@comment-25600444-20180507121446

I guess the ability to reuse a "When this card enters the battlefield" effect with your monsters is extremely good. Heck, Gambit was "nerfed" because of that. It used to be you could cast as many as you want, but now, you can only cast 1 Copy of it a turn.

Plus, it being a Generic Card meant, outside of making more flags that prevent using Generic Cards, future cards released for the 10 main flags were gonna have to always take into account Gambit's re-useability down the road, so they restricted it to limit its influence.