As reported by engadget,
It may seem odd to release yet another slightly improved Snapdragon 865 when the 888 is a more substantial leap and doesn’t carry a huge premium — the 888-equipped Galaxy S21 costs less than its predecessor, after all. The addition might well confuse people wondering why Qualcomm would have such a crowded high-end SoC lineup.
However, the manufacturing might provide a clue. The Snapdragon 870 is built on a 7-nanometer process where the 888 uses cutting-edge 5nm tech. This new chip might not only keep costs down by using older production techniques, but could give phone makers a reasonably fast chip if 888 supplies are tight. You won’t have to settle for last year’s performance in a flagship or upper mid-range phone, even if the gains are very modest.