A part of this is basically growing pains in the meta. Things have shifted and people are now starting to move out of their fire mains they've been in for so long. Light has always been pretty solid, but once people hit level 60 they normally switch (often to fire). Now though, lightning has lots of goodies and solid ninjas to work with so you see many folks switching back over. Even the holdouts are finding it tough as a fire main to deal with all the lightnings because their control wont work on them. Also, you can't out glass-cannon a lightning as a fire. That was a very popular strategy and with the combinations of tobi nerf and fire main side-grade (I wont call it a nerf but I wont disagree with anyone that does) it just seems like they are in a rough spot.
Wind main is actually not that bad now. They have some new goodies to work with and tons of new ninjas to make them great. Azure is great right now but part of me suspects her kit may be slightly bugged so we shall see. One of my guildmates runs mei and windmain - his team can actually outnuke mine as a lightning. Several other winds can give me a good run for my money.
The main draw here though is that Earth main is really in a rough place. Before they could stall out light past their buff periods and then win a war of attrition. That is not a thing now. That combined with the strange place scarlet blaze is in now (along with some ninja nerfs) and the new lightning goodies and synergies gives this appearance lightning is just on an unbeatable pedestal.
Lightning is good. You will see lots more lightning players because of that (just like you saw so many people playing scarlet blaze for awhile). But it's not unbeatable. Root does not last forever, and only affects three sword ninjas if I recall - not the full team. Don't try to out glass cannon them, you will most likely lose. Try out wind main sometime. And don't forget that these new lightning buff fields from danzo or darui can be overridden by the old mystery field changers (one case where old tech can trump new).