Actually, conceptually, it's very logical. The logical concept? Simple.
All gp10 items give bonus stats OTHER THAN gp10.
(This is just how Riot designed the game. There is no why. This is like saying why do all champions have abilities AND passives? --Because that's how Riot designed them.)
Building on my previous point, this specific gp10 item is for ad carries(adc's or champions like tryn). Other gp10 items like spellthief are optimally designed for mages playing support. Spellthief is not popular among mid lane champions because it is inefficient, and provides a very LIMITED, WEAK BUILD PATH UPON UPGRADING. Also, the gold generated from this item is mostly granted to you upon attacking an opponent, where as in mid lane, you will lose the trade so poorly due to the lack of combat stats it provides compared to other options. It is simply not META(most effective tactics available). While avarice blade's passive gold is granted through farming, not fighting. In some situations, this IS meta. Below is an explanation of a situation in which building avarice blade into Youmuu's can be the most effective tactic available.
*Note: because this is a situational item, I gave an example of why a Pickaxe could be a better option.
**You said nobody made a claim for
. Here is one.
-----You build Youmuu's primarily for speed, AND if the stats of ad, armor pen, and crit are OPTIMAL for your build.
-----------Example: Master Yi. Master Yi loves all those stats. He loves to crit, he loves ad & armor pen. He loves to move fast too. But why does he need crit? The crit helps simply helps him clear monsters in the jungle, and extra combat stats for dueling champions. There is no missing last hits in the jungle(unless it gets stolen of couse--but this is why you have smite to secure opjectives). This is a logical example of building Youmuu's out of avarice blade. If you want an explanation for static shyv I can make one too, but I feel like it's much more obvious and easier to find an ideal situation to build it in compared to Youmuu's.
Also, if you have any questions about specific cases then please specify them and I'll be happy to help if I can.