There are a couple different reasons this can happen that I have seen.
The hood latches on each side mount into the sheetmetal on slotted holes so that the position of the latches can be adjusted. If a latch is in the wrong position it can be hard for it to release (or sometimes also hard to latch). I have had good luck adjusting them by loosening the three bolts, partially closing the hood to let the striker pins move the latch to wherever it should be, then carefully re-tightening the bolts in that position to relocate the latch there.
The other way it can happen is if the hood release cable slips at its midpoint attachment to the left side latch. The way it works is that there is one long cable that runs all the way from the interior release lever, hooks up to the left side latch, then continues on to the right side latch. However, if this happens usually the result is that the right side will release but the left side won't. Since you have the opposite situation I would guess it's just the right side latch being misadjusted and probably now also in need of lubrication after sitting for a few years, which is likely the reason it's more of a problem now than when you last dealt with it.
You may be able to get it to release by pulling a little further on the release cable. The release lever will only pull so far, to about 90 degrees. It will break the lever if you try to pull the cable further using the lever, but you can get a pair of vise grips on the cable behind the lever and get another few mm out of it like that. That will usually pop a tight latch free. You might need to have someone pulling up on the right edge of the hood at the same time if it's more sticky due to lack of lubrication or corrosion.
Good luck, as you can probably tell I have had to fight a few of these before and they will eventually open up with careful persuasion and a helper. If you really get desperate or in a big hurry without a second set of hands available you can bust apart the plastic front grille and get access to both latches and the midsection of the cable that way, but it's nice if you can do it without destroying anything.
Used replacement grilles are not hard to come by if you have to break thru it though.
Edit: some better tips than mine in the Brickboard link posted above that must have landed while I was writing this, sounds like maybe the first thing to try would be tightening up the threaded fine adjustment of the cable free play that's behind the lever, I forgot about that.