You are really picking at straws here to justify being mad. Most storefronts, Steam included, take 30%. Humble is also pretty transparent about how the money is divided up. When you attempt to adjust the Humble slider you will notice that part of the bar is grey. This is the fixed minimum cut that Humble has to take for operating expenses.
Edit: typo
These aren’t percents of a total - they are ratios relative to each other.
For simplicity let’s say teach bar has a Min of 0 and a Max of 100. NOTE that there are no units. Bar 1 is set to 100, bar 2 is set to 70, and bar 3 is set to 0. This is absolutely valid. What this means is “for every 100 units sent to 1, send 70 units to 2 and 0 units to 3”. In this case you can assign currency as the units. “For every dollar sent to 1, send 70 cents to 2 and 0 cents to 3”.
Because your eshop sucks ass.