It’s because trickle down-style policies give more wealth and social power to those at the top while allowing the argument that the economic activity that results from that wealth benefits everyone down the pyramid (which also creates a dependency on more instances of these transfers as businesses grow to accommodate the extra demand).

Social programs do that without giving more wealth or social power to people at the top.

The effectiveness that they care about isn’t the economic benefit or allowing people to become more independent, it’s about funneling money to the rich in the hopes that they will funnel some of it back in a way that won’t look so much like corruption.