It's probably because it's tiring to talk about. This has been brought up before, and it always boils down to "I don't like these aspects that Colors introduced" and "I do like those aspects/I think those aspects are fine in Colors" back and forth. There's no point in responding to "Wisps break up the gameplay and became an annoying mainstay of the series" with "I enjoy the way the Wisps are integrated into the level design and story of Colors regardless of their later implementation in other games", because the rebuttal is "Wisps break up the gameplay and became an annoying mainstay of the series". Also, Planet Wisp's failings in Generations almost certainly come from Generations and Colors having a significantly overlapping development period and Planet Wisp being one of the final additions to Generations. The big giveaway to me is how the Spikes and Rocket Wisps in Generations have weird, detrimental subtle differences in how they control and function compared to in Colors.