Arthur found the request made by Manuel II to be quite troublesome.
It wasn't that Arthur still held a grudge over the war with Portugal. Considering that Australasia had won the war comprehensively, if there were any grudges, they should be on the part of the Portuguese.
The main issue was that Arthur wasn't sure whether Manuel possessed the means and capability to rule Portugal.
If they were to help Manuel ascend to the throne, only for him to be overthrown by the angry Portuguese people again, then that would be a big joke.
It was like a political investment, where both parties would profit from a victory, but a failure would also have a certain impact on Arthur.
Although the government would firmly carry out his orders, this kind of action, merely to restore other countries' royal families, was clearly a bit too selfish.
If the country couldn't gain enough benefits, Arthur wouldn't proceed—even if it required just a thought of his.