My thought is that if a team can afford to not have the TE blocking, it is better to replace him with an out right receiver. If they can't afford to not to forgo the blocking of the TE, they can't pass to them obviously.
In theory, it is easier for a LB to cover a releasing TE on a pass route while also covering the run than it is to cover a WR in the slot and a RB up the middle.