Why? It's a step in the right direction imo.
It devalues the competition even further. The UEFA Cup used to be a prestigious competition that teams were desperate to win and often had line-ups that were as strong or stronger than the European Cup. But the expansion of the CL, the ridiculous changes to the format and the tacky rebranding have all contributed to making it a naffer competition than it was. Then you take into account the lack of prize money in the modern game and you're left with a shell of a competition.
They'd be better off improving the actual competition (less bloated format, spread the CL money out) but instead they've tacked on the prize of playing in the real competition that UEFA cares about. They've basically admitted its rubbish rather than trying to fix it, and stuck on an incentive as an easy fix. When WINNING A TROPHY needs an incentive of playing in another competition to make it worthwhile surely that should tell them that they've fucked it up completely somewhere along the way.
Over the next few years it status will fall to being no more than a 4th place finish equivalent.