Why did they nerf this?

Some would argue that a perk every level in F3 led to the PC being overpowered. I tend to agree. In NV, it's generally harder to buff out your character, and it's not by mistake.

Agreed, perk every level will lead to an overpowered character. Besides, with all major DLCs level cap is 50, meaning 25 perks in total which should be enough.

Yeah, if you're thoughtful about what perks you choose in F3, it isn't long after you get your feet underneath you (a few hours after leaving the vault) that you start becoming overpowered, which takes a lot of the challenge out of the game.

My initial reaction to not getting a perk every level in New Vegas was "wtf is this?", but it (along with fewer buffing options like skill books) led to a more challenging game, which is more fun in the end.