It's because intentional feeding isn't what you think it is.
It's not intentional feeding if someone ignores the call you made to group and dies for it.
It's not intentional feeding if they initiate when you want to retreat.
It's not intentional feeding if they try to contest a baron 1v5 and die.
It's not intentional feeding if they get jumped in the jungle and die.
It's not intentional feeding if they keep losing trades in lane and die.
It's not intentional feeding if they lose a trade in mid against a Zed and then get 100-0 killed under tower by that Zed.
It's not intentional feeding if they come to help a losing lane and give up a double kill.
It's not intentional feeding if they chase too far and get jumped and die.
It's not intentional feeding if they get outplayed.
It's not intentional feeding if they don't build the items you tell them to build (see: AP Garen Rule or AP Vayne Rule)
It's not intentional feeding if they get a lag spike or a frame rate issue and die from it.
All of those cases boil down to "that person thinks they're right and you're wrong". And whether you're right or they're right, it still doesn't constitute intentional feeding.
intentional
[in-ten-shuh-nl]
adjective
- done with intention or on purpose; intended
Additionally:
It takes a specific X value, where X is defined as report value per match, or a Y value, where Y is defined as total report value in 10 matches, for a person's case to appear before the Riot staff. This is why veteran accounts who haven't been in trouble since beta are less likely to be banned than new accounts. Y > X in this scenario, i.e. it takes a lot more reports for a small window to bring it to Lyte's desk than a lifetime toxicity value.
Imagine two players play in matches. Both players obviously intentionally feed -- they pick Master Yi, get 
and stack 
, and run into the enemy towers near a player as fast as they can immediately after every respawn. Let's assume everyone playing in these matches has an equal report value (1).
Account A has 50 games lifetime.
Account B has 5000 games lifetime.
The X value for Account A (if this is his first report) = 9/50 = 18% toxicity.
The X value for Account B = 9/5000 = 0.18% toxicity.
A will get banned, B will not.
Your report value has a complex formula, but it can be crudely modeled by the equation RV = 1 + [(Correct/Total) - 0.500].
If you report and your reports result in punishment, your get a 1 added to Correct and a 1 added to Total, raising the value of C/T and thus your RV. If you report and your reports don't result in punishment, you get 0 added to Correct and 1 added to Total, reducing the value of C/T and thus your RV.
It's the boy who cried wolf. The more often you cry feeder, the less anyone cares when you cry feeder. So, when you get an actual feeder, your report means so little that you're literally helping the feeders get away with feeding.
