I assume it was part of the sweeping changes made to nerf recoveries. Honestly, between that and the ledge snap reduction, ROB's recovery got way more predictable. Picking stages with a high top platform to recover to safely are going to be more important in 3.5.
Most importantly, though, is that it takes away wavelanding out of the third boost, which affects not only recovery, but also the neutral; I used to tomahawk grabs out of boosts as a mixup, and now that option isn't there if I decide to dash dance my boosts. Even though that's a niche situation, taking away that option sucks a little bit.
Overall, though, some characters were hit way harder than ROB, and we even got a slightly bigger shield now so that maybe we won't be instantly shield poked even at full strength. Even if ROB is very very slightly worse now, (which, even that I think is debateable), his strength in relationship to the other characters is higher than in 3.0.
Edit: After playing around with ROB for a little, I've discovered that he actually can waveland out of his third boost if he's almost touching the ground. Like, "Almost landing by default" nearly touching the ground. Not sure how practical or even reliable this is, but it's something I guess.