The two configurations I can think of:
The jet mounted on the horizontal stabilizer (above, below, at the tip):
Unlike the vertical stabilizer, the horizontal stabilizer is trimmable (THS), so all of the engine connections (fuel, hydraulic, pneumatic) will need to be made flexible and/or pivotable, which results in added complexity and points of failure. And, the longer lateral placement of the engines will considerably increase the weight; a standard THS mounting (just two points for pivoting) is not built for transferring the thrust to the airframe. This also impacts the loading flexibility; a very tail heavy plane can't have as many passengers in the back without adding a forward ballast, further increasing the weight.
The jet mounted at the root and doesn't move with the THS:
While certainly achievable, like the L-1011's number two engine wrt the vertical stabilizer, the issue here is not why aren't the jet engines there, it's why the THS is not there.
The horizontal stabilizer of a plane like the DC-9 (and its extended family) is purposefully placed above the tail, creating a T-tail. With the tail swept back, the top of it is farther from the plane's center of gravity, giving the THS a bigger moment arm, and in turn allowing a smaller THS, and the other benefit that comes out of that is the end-plate effect of the T-tail, which also permits a shorter fin for the same control authority.
You'll also notice buried engines are of the older small-diameter type, except for large planes like the L-1011, but still that makes maintenance access a lot harder, than an exposed engine.