Because they need to be the smartest babyboys in the room, and if everyone has a simple solution, then you can feel really smart if you can point out how it's not at all that simple actually. It's literally all their policy.
"Israel-Palestine is complicated." No it isn't, stop funding colonial settlers doing genocide.
"Homelessness is complicated" no it isn't, give them homes.
"Starvation is complicated" No it isn't, we produce more food than we need and throw most of it out before it even reaches a store. Give it away.
"Healthcare is complicated" no it isn't, make it universal like everywhere else
"Education is complicated" no it isn't, make it free
"War is complicated" no it isn't, stop doing it
"Water scarcity is complicated" no it isn't, stop having golf courses and stop growing pistacchios in a desert
"Public transport is complicated" no it isn't, you're just wasting all the money on financing the private automobile industry
"The massive prisoner population and wrongful incarcerations and shitty courts is complicated" no it isn't, you've privatized prison and you're using slave patrols to uphold the law. Don't do that.

Libs like to pretend like this shit is complicated so they can feel cleverer than the people that say the things are simple. Now if these things actually ARE simple, then the libs would turn out to be fucking idiots.