Why did the US Supreme Court hear this case?

Question

An op-ed entitled A Major Church-State Ruling That Shouldn't Have Happened claims that

In Trinity v. Comer, there was no remaining dispute between the actual parties

As I understand it, courts have no power to seek out cases or issues to rule on. A party with standing must bring the case to the court. (I've usually heard this in response to rhetoric about "activist judges.") So either my understanding has been wrong, or there's more to the story of Trinity v. Comer.

If there was no remaining dispute, why did SCOTUS hear this case?

Answer 1

The explanation in the decision (fn 1) is that

That announcement does not moot this case. We have said that such voluntary cessation of a challenged practice does not moot a case unless “subsequent events ma[ke] it absolutely clear that the allegedly wrongful behavior could not reasonably be expected to recur.” [citations] The Department has not carried the “heavy burden” of making “absolutely clear” that it could not revert to its policy of excluding religious organizations... “there is no clearly effective barrier that would prevent the [Department] from reinstating [its] policy in the future”

Answer 2

This is quite unusual and it is not unheard of for SCOTUS cases to be dismissed because they become moot during the course of the proceedings.

It could be that no one advised the Court that the case was settled and moot, perhaps because both sides wanted to have the legal issue resolve for posterity.

There is an exception to the mootness rule for circumstances that are likely to alway become moot but are likely to recur if not ruled upon because the events involved have a shorter timeline than the court process. Many abortion cases and cases involved the rights of school students have this character, but this one is not an obvious example. Perhaps the suit is still valid under this doctrine because it involves grant applications in a different budget cycle.