Source: The Wrestling Observer
It's being reported that Brian Kendrick's WWE release was actually something that had been planned a few weeks in advance, which is why he had been so negatively booked on Raw. In his last couple weeks on TV, Kendrick was booked to lose to both Jerry Lawler and Kofi Kingston in what were basically squash matches meant to humiliate him, and that was the way WWE wanted him booked prior to his release.
It's being said that Kendrick failed numerous marijuana tests and WWE management was getting tired of his repeated failures. Although a marijuana test failure only constitutes a $1,000 fine as opposed to a suspension, WWE is cracking down on the wrestlers who abuse the drug too often and repeatedly fail tests.
Kendrick's release is not only punishment to him for failing marijuana tests, but it is also being used to serve as a warning to talent higher on the card who feel they can get away with abusing marijuana and simply pay the fine when they fail a test.