Because his aura had clearly reverted to that of a regular SSJ. In some panels where he's standing in front of Majin Boo with no lightning, he still has the fiercer aura of SSJ2.
Ah yes, Vegeta also gone back to SSJ to knock back Trunks and Goten, even though, Majin Buu could've appeared at any point and had already massacred him, Vegeta only went SSJ2 against Kid Buu in the beginning when he was throwing blasts at him and went SSJ back even though he has to resist his punches and survive, the lack of lightning is absolute evidence.
The lightning disappeared only when he massively enlarged his aura in preparation for launching the KHH. This was intentional, to convey that he was giving off a ton of light.
This is intellectualy dishonest at its best, Cell didn't have electricity during the whole beam struggle since it began to its end.
Which are such a small portion of the total number of panels in which SSJ2s are depicted that they are the clear outlier. Again, show me a consistent example (~ chapter long or more) of SSJ2s or SSJ3s lacking lightning entirely, in chapters in which they are the star character and not just some dude occasionally shown in the background. Other than Vegetto there is no SSJ with lightning, and when there is lightning it's only for one panel, so that the reader can grasp just how powerful this regular Super Saiyan is. In the entire run of the original manga there hasn't been the inverse - SSJ2/SSJ3 characters lacking lightning for an entire chapter or more.
Gohan didn't have lightning during the whole beam struggle since it ever began to its end with Cell, obviously because I can't post that much images I can't show it.
Toriyama clearly intended for SSJ2 to have traits to distinguish it from the previous form, which can be seen in Goku and Gohan even without lightning unless you're blind. Goku's bangs covering the forehead all stick up and his hair becomes more wild and rigid. Gohan's hair which was only slightly spiked up from his regular form all sticks up and becomes wilder other than the one covering his forehead, not to mention both of them have lightning constantly surrounding their auras and the auras themselves become far more pronounced. In no instance in any Toriyama-drawn manga (until the gag manga Neko Majin) did any regular SSJ have any of these traits for longer than one lone panel. And Kuririn's shock to seeing SSJ2 Gohan (after having already seen the full power of his regular SSJ form) shows that the form's difference in power and aura intensity is immediately noticeable, Babidi just can't sense Ki because he's a retard.
Ah yes, I win the argument because I called the characters retard and I give an "hahaha" hurr durr, immaturity at its best you reflects here.
I don't know what kind of requirement it is for someone to need to be able to sense ki to realize that someone has changed appearance-wise, seriously. Even Bulma could tell how much Trunks changed after his training in the rosat, despite of the fact that she can't sense ki.
Ah yes, even though, even in Super, Beerus asks himself whether SSJ2 Goku changed that much or not in relation to his SSJ and how Goku Black/Zamasu talks about SSJ2 Goku as Super Saiyan Goku, even though it is visibly a SSJ2. Everyone is idiotic hurr durr.
