He was by all accounts a quarrelsome, arrogant and assertive man, who clashed with most of the leading Irish political figures of his time.
Apart from the question of where his real loyalties lay, MacCerbaill had a practice of consecrating bishops without asking for the King's consent, which naturally irritated the monarch.
In fact, it is simply evidence of his turbulent nature: he also quarrelled in the 1260s with his successor as Dean of Cashel, Keran (or Kyran), who accused him of cruelly ill-treating the clergy of the Archdiocese, and of despoiling the deanery.
The Dublin administration was utterly indifferent to the proposal,[1] and there were obvious difficulties with collecting so vast a sum, despite the Archbishop's best efforts, given the chronic shortage of money in Ireland.
The King himself may have had doubts about the feasibility of the project, particularly, as his biographer suggests, if the price was whittled down to the point where it meant that the Irish would get the benefits of the common law for free.
[1] Mac Cerbaill, arrogant and quarrelsome to the last, was engaged in a dispute with his fellow bishops when he died in late July or early August 1289.