The late 90's early 00's saw a boom in Receiving TEs, and many weren't great at blocking. Defenses caught up.
Elite TEs now have to be able to do both - see Gronk and Kittle. Kittle's blocking skills are close to those of actual O-linemen. You can't go speed on D if the TE can block you off the field, but there aren't many LBs who can cover big TEs that can run crisp routes with soft hands. It opens up the field deep for the WRs if the team has to double a TE, or use a Safety to cover.