In The Flash TV series, why can't the Speed Force itself defeat Zoom by taking away his speed?
P.S. I am not a comic guy!
The mechanics of the Speed Force are currently beyond our comprehension, since Harrison Wells was able to "remove" Barry's connection to the Speed Force and allow Zoom to "absorb" that connection, growing faster due to his claim to that speed.
Unlike the comic version of the Speed Force, a non-speedster using vibration-based powers could conceivably reach and open a doorway to the Speed Force, even if they could not enter the "Speed Dimension."
It may be beyond our comprehension as to why it ever shared the Speed Force with any Human but it appears unlike the comic version of the Speed Force, this one is apparently able and willing to communicate with a speedster, if it desires to.
In the comics, the Speed Force is a subset of a greater Universal power called The Source. Often depicted as a barrier to the edge of the Multiverse, the Source Wall imprisons any who try to plumb the secrets beyond the Multiverse, which it presumably protects.
The Source is believed to be the primal energy of the DC Universe, powering all aspects of metahuman capability and the boundary to what is believed to be the DC Universe.
The Source is responsible for the "Godwave" a primal distribution of metahuman energies including the Speed Force, the Quantum Field and the emotional electromagnetic spectrum abilities of the Guardians of Oa and the other Lightsmiths.
Zoom's movement power isn't based on speed, it's based on time. He moves through time at a different pace than everything else. He doesn't really go that fast, he just completes what he's doing ahead of when he should.
In the comics, one side-effect of his power/condition is the proximate generation of little wormhole visions of his past. The Flash forces him into contact with one effectively tying his timeline "in a knot", and basically freezes him in time.
Edit: This is the comic-relevant answer, from which the show seems to diverge. Perhaps it will become more relevant as the show progresses.
We learn about the complete backstory of Zoom in the season finale of the second season:
Zoom gets his powers like Barry, by the combination of the radiations of the explosion of the particles accelerator and an electric shock (by an electric chair in his case).
But he was power-hungry and used the Velocity serum to increase his speed and
tried to "break the rule of the Speed Force". The precise meaning of this, beyond the use of the serum, is not revealed. We only know that he travelled through time and through different Earths.
Things go wrong as the Velocity serum made him dying and
he loses its connection to the Speed Force. His speed at the beginning of the episode is coming from the Velocity serum.
This leads to the events of the Season 2, where Zoom tries to steal Barry's speed, hoping that it will cure him/make him the fastest speedster of the multiverse.
In the finale, he is finally defeated,
taken by Speed Wraiths, that were hunting him for some time, in the name of the Speed Force.
Because people are curious. People have free will. The Speed Force did not cause a particle accelerator explosion. It was the Wells(es). With actions come consequences.