Notice the title. It's not me saying that TDM should or needs to be more than 100 kills, it's simply a reason or argument for a change. I don't know how I feel about raising or lowering the kills to win so I'm just going to give my reason and watch the debate unfold.
TDM is looked at as the purest gamemode in Call of Duty. The objective is simple and straight forward, be the first team to kill 100 enemies. What I think players like most about TDM is that the limited points earned and the low number of kills accumulated keep the focus on gun v gun combat.
I have a good bit of TDM matches under my belt and I can say that several dozen times a match of TDM has ended with me only 2 or 3 kills from a really high streak like Dogs or a SWARM. Those matches I played a Hell of a game and there's nothing I could really have done differently to have a better game. Point is TDM doesn't facilitate anything more. You're doing really well to earn anything over a Stealth Chopper and the fact that you can't call in any Scorestreak is why people love TDM so much. Increasing the kills only increases the chance of having superpowered airsupport ruining the purity of the gamemode.