The potential gold you can get from Cull is 100+300+180= 580 - 450 = 150 G. So you get 150 G if you cs perfectly at 11 minutes and if you forsake the extra stats of the a Doran's Blade. 150 G. That's practically nothing, but that's your **potential **gain.
On the other hand, if you opt to start a Doran's blade instead, you get 80 HP and +3 AD and 3% lifesteal that greatly compliments the new mastery changes and can scale. These small stats that you gain by choosing Doran's Blade instead of Cull are vastly, immensely, and exponentially more valuable than the measly 150 G.
Most people hang on to their Doran's for a long time. That's how valuable and gold efficient it is. The lane phase power that Doran's Blade offers is too much to ignore. Why would anyone want a potential +150 G when they might lose just as much or even more gold because they were denied CS in lane as a result of Cull being weaker than Doran's Blade?
If cull could upgrade, however, then it might actually be worth while. It makes sense for it to upgrade into Vampiric Sceptre both stat wise and visually even. So, why doesn't it?
Either do something about Cull or remove it from the game. It doesn't add any strategic diversity or a meaningful choice at all.