I saw some videos on youtube where people modded dev spells into the game. Why were these cut?

Do you have a link to those video? They're probably custom made spells by modders.

I dont really think they have cut any out, except for the test spells, I have seen all the spells with spb and it looks like they are all in

Most spells you're talking about are either test spells, or non playable spells that are the abilities of the monsters that you fight;

Such as waterwalking for spirits.

They were on console, so I don't think it is allowed.

They were probably spells made by modders

They rid cut out a lot of spells that was in past games.

but you just said that they were modded back into the game

The guy said that he modded a saved game and put it on his xbox. I found while searching for mods for my new laptop.

I've seen lots of videos of nifty new spells in Skyrim. Not a single one was of console gameplay. The videographer may have been lying. People do that on the internet all the time. If you provide a link we can look for graphical signs of it being PC gameplay.

The spells are generally creature abilities, or intended as noncastable effects (enchant/alchemy effects), or are spells only intended to be used in scripted events, or are implemented as once-per-day stone abilities and not standard magic. I doubt any of them were originally intended as PC-castable spells in the conventional sense.