WHY does the prestige/ranking of your law school matter?

I hear all the time that the ranking/prestige of your law school matters a ton, but why? Is the quality of education substantially superior at better schools? Is it the network that you develop? Can someone lay out the reasons why your law school's prestige matters? Genuinely curious.

I'm not asking about predatory schools- those are a whole different ballgame and suck for obvious reasons. I'm talking about why people turn down full rides at T20s to attend a T6.