That's the way it is meant to be.
In a Hybrid the electric side is there to help the ICE side. It's not going to run electric all the time and will swap one mode for the other as it sees fit. You should be able to hit about 16km/l if you just drive (at least that's about what I get in my 2015). I find that for me on an average trip 1/4 to 1/3 is on electric power.
A Plug in Hybrid is the same, but with more electric (still only about 40-60km at most). It'll run electric when it can but will still switch to ICE as needed. There is a plug in C-Max but you loose about 20cm in depth for the cargo area as the battery is bigger. You would be on electric a lot more as most people drive under 60km on an average day. From what I understand, it'll fully recharge overnight.
The closest full electric to a C-Max is the Chevrolet Bolt EUV. I parked next to one and they are almost identical in size. It looks like a good car.