Why aren't there V-tail airliners?
Controllability and redundancy. Airliners are certified according CFR 14 Part 25, which specifies that upon engine fail the aircraft must still be able to fly and climb: it must have more than one engine.

After an engine has failed, the rudder must be deflected in order to compensate for the asymmetric thrust of the remaining engine. With a V-tail, this means that after engine fail, there is less pitch authority: pitch and yaw surface deflections are coupled. A V-tail has two control surfaces that combine aircraft yaw control and pitch control, which goes well until one of the surfaces hits a stop.



Reduced pitch control due to an engine failure would be unacceptable for an airliner. For a single engine plane with the engine in the centreline, this yaw trim condition would not happen.