Upmarket bodhrans do have tuners, like those on Turkish metal darbukas.

I'm not quite sure what bodhranists are aiming at when they retune. The sound they usually prefer is a dull thud - i.e. they detune enough that no definite pitch is perceptible, but leaving enough tension on the skin to get a reasonably loud sound. This is quite different from what most Middle Eastern frame drum players do - they either select the drum or tune it to get the highest, pingiest sound possible. This goes along with a different philosophy about what the drum is for. In a Middle Eastern band, it drives the whole ensemble; the drummer is effectively the conductor. (In Sufi music, the kettledrum has the central role, and is understood to be a metaphor for the creative energy of God). But bodhranists seem to want to produce such a vague, blurry sound that they could never take the lead and nobody listening could ever tell when they made a mistake. It's an aesthetic of timidity. What do they get out of this?