It was to my understanding that part of it was that they didn't want boosters and account selling anymore, but I don't see how that balances out the issues that come of not having both a continuous exterior motive for winning a match (because the progression system will undoubtedly finish at some point) and staying within a match even if you're losing (because you can receive a hit on your overall skill ranking).
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Because Bungie realized that H3 was very competetive and they wanted to cater to the masses (who are largely casuals) so they could get more sales.