There are multiple reasons this hasn't, and shouldn't, be implemented.
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You would have to do the reverse as well. If someone on the enemy team is int'ing you would have to not gain as much LP for a win. Without an equal balance, there would be an inflation of overall LP gain which comes with its own issues.
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It would encourage more reports and flood the report system even more than it is already. If people knew they would lose less LP for an inter, they would be more likely to report people that just had poor games, on the off chance that it would lead to less LP loss.
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It takes awhile to review and punish these players. It would be tough to retroactively restore LP points in a fair system that accounts for all possible complications (demotions, promotions, etc).
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At the end of the day you will gain more LP than you will lose from Inters ON AVERAGE. Just the way it is and the way the math works out.
Inters suck, but this isn't the solution and has been suggested many times.