fish spawning ?

I need a little help here with fish reproduction. I tossed a few feeder
goldfish into my pond 5 years ago when I dug it. They produced a 2nd and
3rd generation each successive spring, and some of the original fish were
lost to racoons. There are currently 7 or 8 fish in the 600+ gallon pond, a
few from each generation.

My question is this: for the past 2 years, I've had no new generations.
Why?

The last 2 years, I started vacuuming the bottom of the pond regularly
during the growing season (no bottom drain); I'm just vacuuming the very
bottom at the deepest part. I've also added frogs/tadpoles the last 3 years
(6 tadpoles yielded 3 frogs over the years). And I have still seen the
chasing-the-one-fish-around activity that I assume was mating related.
There are plenty of plants in the pond year round (z5), including underwater
plants.

So? Is the chasing not mating? Do I just have all one sex? Are the
additional pond inhabitants eating the babies before I see them (there's
usually a dragonfly nymph or two in there by spring as well)? Am I
vacuuming them up? Do I need to pipe in some mood music next spring?