Warp strafing, why isn't it used more?

[Borgholio]

From Memory Alpha:

The propulsion system of the torpedoes is a warp sustainer engine. The engine coils of the torpedo grab and hold a hand-off field from the launcher tube's sequential field induction coils. A miniature matter/antimatter fuel cell adds power to the hand-off field. When launched in warp flight, torpedo will continue to travel at warp, when launched at sublight, torpedo will travel at a high sublight speed, but will not cross the warp threshold.

This basically states that the torpedo actually has it's own warp coils and they are energized with a warp field created by the launcher itself, not the ship's warp field. So that kinda implies that a torpedo would travel at warp speed IN THE DIRECTION it was launched. Although this quote is from the TM, it's the best actual description we have.

[Prometheus Unbound]

Well presumably yes, in the direction they were launched.

Keh'Lar's probe / torpedo was shot out at warp 9 from a station.

And they were firing in reverse in E&F.