What Happened to the Spammy Posts
The two posts you referenced were addressed by the community, but insufficient action was taken by users with sufficient voting privileges. I eventually deleted those questions outright, rather than treating them as spam, for the reasons outlined in the accepted answer to a related meta question.
Flags can and do age away. This is by design. Long-time users of Stack Exchange might worry about flag weights associated with incorrect flagging or flags that lack critical mass or moderator action. Don't.
Flag-related hell-bans and flag weight in general have been gone for a long time. I don't even think there are any consequences at all for flags that age away, but if you run across some please raise them on meta or contact SE support, as they shouldn't exist.
Mostly, flag aging is a reflection of our (relatively) small community, and the fact that moderators try not to get involved too early because (most of) our votes are binding. So, in many cases, low-eyeball issues that haven't attracted critical mass will age away, but helpful flags remain helpful even if they are not longer counted towards critical voting mass. They help moderators and staff down the road, even if they don't solve a problem today.
In short, I can't see much of a reason to worry about flag aging. If you think something needs more attention than it's getting, bring it up on meta!
I didn't look closely at your other examples, except to note that they are newish. The flags are less than a week old, and on this particular site even the avid users are generally out of pocket nights and weekends. So, you need to give the community (meaning all the users with access to the review queue) a chance to review the flags. There are flaggable problems that need immediate action, but in my opinion "low-quality answers" aren't among them.
On a side note, "not an answer" is also intended for posts that are off-topic or (most commonly) attempts to comment or ask related questions rather than answer the original post. It's not the right flag for answers that can be improved, or even questions that are factually incorrect. Bad answers need to be policed by the community as often as possible, and diamond moderators are here to handle the cases where the review system or voting system lacks critical mass.
I often see "not an answer" used incorrectly, and at least one of the questions you flagged would seem to fall into this category. That doesn't mean the flagging itself was invalid; it just means moderators may not take action on an incorrect flag, and the community may not agree with your flagging reason.
Overall, I think you're doing a good job drawing attention to problem posts. Please don't let flag aging get in the way of your conscientious attempts to keep the site litter-free!