Why is the relic shield line the only one where you have to fully upgrade it

To get the most gold generation from the passive(not the gold per 5/10 second part)? Note: I'm not saying nerf coin/spell thief line and buff relic shield line. I'm curious as to why the items are like this. The coin and spell thief line only need one upgrade to get the full value of the gold generation. Upgrading the item to the last stage doesn't increase how much gold you generate from their passives. For the relic shield line however, you have to fully upgrade it to get the most gold generation in terms of another minion execute charge(4 total when fully upgraded), charge rate(takes 20 seconds to generate a charge vs 30 seconds from the first upgrade), and the minion execute threshold(how much health does the minion need to be at to be able to execute with an auto as a melee champion). Is there a reason why the relic shield line requires the full upgrade for gold generation while the others only require the first upgrade?
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