What's the actual point of turrets these days?

Enemies need to destroy turrets before they can take your nexus. Defend the turrets so that your nexus isn't destroyed.

Rock is in short supply so they started ordering paper mache and paint to make new ones. Honestly new turrets every game is expensive to build, supply lines in Runeterra are sketchy with inflation the way it is. Economies down too, you could blame stock investors but who wants to make investments when the Noxians are always talking about war this and war that. It's not healthy for a global economy.

Turrets really should be buffed honestly. I got dove by a level like 9 Olaf earlier and he took a solid 8+ turret shots after being half hp and he got out fine