I do not know why Ont. government would leak the other items of prospective budget but I
perfectly understand why with respect to the Ring of Fire.

The Feds probably have not commited to Ontario a specific dollar amount so Ontario can not specify anything definite either. The reason is that Ontario does not want to commit, for example, to 100 million and find out later that Ottawa will only fork over 50 million as it's share.
I think Queen's Park wants an even Steven split with regard to financing so expects, even if privately, for Ottawa to say how much they are willing to fund.

Queen's Park leaks so that it is out in the open that they will fund and expects an indication from ottawa how much they will so that Ontario can match it and place the amount in the budget.

Without a definite commitment from Ottawa, the Ontario budget is in limbo re the Ring.

This is from the peanut gallery ( i.e. the cheap seats, lol).

p.s. Our sp now reacts to the leak of Ring possibly being mentioned in the budget.