There are multiple reasons for different fee spikes. So when you see fees going up, it can be because of one or more of these reasons:
1. No blocks having been found for a longer than usual time
Because of the way PoW works (you may get unlucky and not find any blocks), there are times where no miner finds any blocks for a while. It could be an hour for example, which means instead of having found 6 blocks (1 per 10 min) only 1 were found so 5x block_tx_count transactions would be left unconfirmed therefore creating a congestion.
This one doesn't last that long since the congestion is not that big and they are rather rare.

2. Major price movements
Whenever price goes up or down, suddenly and big, a lot of traders move their coins to and from exchanges. That increased on-chain activity increases the "demand" for the limited block space therefore increases the fees.
This is why we always have congestion during big bull runs. And these ones last longer than #1 but the duration depends on the market activity.

3. Spam attacks
Spam attack is basically when an entity or a group starts intentionally injecting a large number of transactions into the mempool that serve no purpose other than creating a congestion. I recorded some of the cases a couple of years ago here.
These types of congestion can last a lot longer than any others because they are intentional.

We can categorize abusive transactions such as those involved in the Ordinals Attack as a spam attack as well because they did the same thing by abusing the system.

Yes, that would be reason #2