The NFL claimed they did research and a lot of the impact injuries they want to avoid came on kickoffs, hence the changes.
Latest round of changes penalize touchbacks and squib kicks to encourage more returns though. New rules make the collisions lower speed but they added gimmick rules to make the game more "exciting." Having a team start at the 35 on a touchback ain't good for the quality of the game. With modern kickers range you only got to go 20-25 yards to be in field goal range off a touchback. Used to be you had to go 40-50 yards.