PO sneakily and illicitly appointed TK judges: 1) to ensure their continued monopoly (PO had hand-picked 14 of the 15 TK members with only 1 for the opposition); and/or 2) PO deseprately needed a pretext to stir up trouble and destabilise the winning camp.
PO incorrectly appointed 2 judges. Three correctly appointed judges are being ignored by the overly partisan ruling party.
And the TK is about interpreting the constitutionality of legislation and so party affiliation should not matter, by discussing the party affiliation of judges PiS is signalling that it intends to appoint judges who will support it irregardless of the constitution - rule of party and not rule of law.
Finally, there's no rule saying the opposition cannot try to destabilize the ruling party. That the ruling party fell so easily for such obvious bait is an indicator of its .... unsuitability for being the ruling party.