There aren’t many ad services that probably pay for a 5 second ad view, as they probably wouldn’t get paid either. So it’s not weird at all. If they don’t get paid, they can’t pay you.
There are many ad services out there though, so you might find something that works best for you.
This isn’t about downloading. This is about paying for an ad view. If I purchase a 30 second time slot and my ad plays for 5 seconds, did I get what I bought? I expect my ad to play the full 30 seconds.
Not sure what games you are playing, but it’s super rare to have an ad you can skip. I haven’t seen that in any of the games I play on mobile.
Not to say it doesn’t exist, but you have to realize every company is going to be a bit different. Some companies don’t use an ad service and could sell ad space directly. Some companies also show ads for other games they have, thus they may allow skipping.
It’s also possible skipped ads may pay on some services, but the amount is small, so unless you have 10000 skipped views, you’ll not even see a penny.
The end result honestly? Unless your game is big, skipped ads may not pay much, if at all. But, you’ll need to see what the ad company you go with does.