You're not hitting the pocket. You think you are because you're not looking close enough.

Stoned 8 pins are the only true right handed tap, mostly because today's balls hit too hard and the pins react too violently. It's a dead flush but the headpin, instead of going into the 2 and 4 and 7 pin, bounces off the 2 pin sideways, directly into the 5 pin. It knocks the 5 pin straight back before the ball hits the 5 pin. Therefore, there's nothing to knock down the 8 pin. The ball normally hits the 5 pin into the 8 pin. So, it sits there laughing at you/me.

On normal right handed strikes the ball hits only the 1 pin, 3 pin, 5 pin and 9 pin. Some recent pundits claim the ball should split/hit both the 8 pin and the 9 pin these days. I've seen it and done it; not 100% sure it's correct 100% of the time.

Ringing 10 pins go too long and hit "behind" the head pin because of their angle of entry. Some actually happen because you didn't hit the head pin thin enough. I've seen thin pocket hit that would normally leave a 10 pin, but the 6 pin comes off the side board (instead of wrapping around the 10 pin) and hits it sideways.

Weak 10 pins are the result of balls burning up a hair too much in the midlane and hitting weakly.

Apparent "solid" 7 pins are a hair too high and the 2 or the 4 pin go spinning around in opposite directions. This is close to the idea of the stoned 8 pin, but it is actually a hair too high. The 7 pin could go, if you got lucky and the 2 or the 4 pin hit it coming off the side board.

9 pins are just high hits in which you were lucky and got pin action to knock down the 4 and the 7 pin. Back in the urethane era, the 4/7/9 woudl be sitting there. Be glad you have only a single pin sitting there.

All of this is due to variations in ball speed, release, and targeting, plus the fact that you didn't get lucky. You need to be more consistent or more lucky, one of the two.

 To "add" to what charlest has stated, learn to watch what the ball does after it initially contacts the headpin, and as it travels through the pins and off the back of the pindeck.

 The path it takes through the pins, and the point at which it leaves the deck, can tell you much about what the ball is actually doing and, perhaps, why one ball carries where the other doesn't.

 It can also tell you which way to go with your ball choices to achieve the best resulting pin action, entry angle, and exit point.

Another suggestion.

If you have a video camera, set it on a tri-pod during open bowling. Have the video just on the pin deck. After watching some of your hits you will see what you ball is actually doing down there. Knowledge is the key. 

 

You've been given some good reasons why it happens, and what to look for, but what to do about it?

Something has to change in the speed, revs and angle that the ball is hitting the pocket - often a very small change in any of these will give the desired effect.

There are some things you can try, all depends on your game and your ability to adjust.

Move up on your approach slightly, this can change the speed and angle just a tiny bit and start carrying single pin leaves.

Change your release slightly, a little more behind the ball, or a little more to the side on release....side revs, or a later drive, both can start carrying when you're leaving.

Change ball...sometimes a similar reacting ball but with just enough difference in lane behavior can kick the pins around favorably.

Lots of stuff you can do. The important thing is to have the tools and comfort with them to address these issues on the lane, as you play them.

i've had several balls now that if i release around the side of the ball even slightly, visually the ball will react the same, but infact it has a different rotation on it, and it's a 10 pin everytime.when i release it correctly behind the ball, it will finish the rack.

Somtimes, I do the opposite if I'm leaving. It depends on the lane. If I'm behind the ball on a long pattern, the angle is wrong or the drive is too strong and I'll leave singles. In that case, a side rotation still works because it skids through the oil and still has enough energy at the back to plow through but with more revs.

And, sometimes I get behind the ball more.

There are a lot of things that individually can cause or fix carry.