The law requires the judgement by the diocesan bishop that a spiritual good of the faithful will be assisted.
Thus, canon 87 §1, "As often as he judges that a dispensation will contribute to the spiritual good of the faithful, the diocesan bishop can dispense from both universal and particular disciplinary laws established for his territory or for his subjects by the supreme authority of the Church. He cannot dispense, however, from procedural or penal laws or from those laws whose dispensation is especially reserved to the Apostolic See or to another authority. "
Dispensation from the obligation in canon 1247 is not reserved.
Further, canon 1245, “With due regard for the right of diocesan bishops which is mentioned in can. 87, for a just reason and in accord with the prescriptions of the diocesan bishop, the pastor in individual cases can dispense from the obligation to observe a feast day or a day of penance; or he can commute it to other pious works; the superior of a religious institute or a society of apostolic life of pontifical right if they are clerical can also do the same for his own subjects and others staying in his house day and night.”
This power to dispense from a day of precept or penance can also be delegated to other priests and deacons, but they would not possess it unless so delegated. Note that pastors can dispense or commute in individual cases. This would not seem to include dispensing or commuting an entire parish en masse.
Finally see canon 89, “The pastor and other presbyters or deacons cannot dispense from a universal or particular law unless this power has been expressly granted to them.” The canon above gives it to pastors and superiors as noted but not all priests.
We do not know Bishop Sample’s reason nor need not know it, but the presumption is that he considered the situation and judged the matter according to the requirement of a contribution to the spiritual good of the faithful before exercising his authority in this matter.