The guitar is, for the most part in Irish Trad music a rhythm instrument. It is much more skilled technique then melody playing, for this type of music - and the guitarist is really the only with with real creative ability, when the band is playing tunes sets. Irish bouzouki or octave mandolin is sometimes used, typically in lieu of guitar, for the same purpose; providing rhythm.

It has nothing to do with player skill. The guitar is a good rhythm instrument, even providing bass for tune sets. And typically DADGAD or similar low modal tunings are used.

.. and as Leadfingers said above, playing rhythm for this kind of music, really takes a very skilled player.