It 'keeps coming up' because it's a strawman people love to punch. People literally only bring up this concept in order to tear it down - because it was only created in order to be torn down.

Nobody actually argues for 'trickle-down' policies. It's a sneer term signifying a deliberately oversimplified version of right-wing economic policies. It's not a real position people hold and push for.

I guess it's a lot easier and more fun to feel righteous attacking strawmen than it is to do the work of interacting with real ideas with serious intellectual backing and real influence.