Here are a couple of thoughts. One is why we double flock, another thought is why we hand paint white areas.
Double flocking is both for durability and getting an even coat. Any of you who have done much flocking will know the look of that first coat. It's pretty patchy and will wear off far sooner than you want. All factory flocking is a single coat and not terribly durable. I have some full curl mallard heads on the way that are worn down to the plastic in places and down to the green glue which is shiny, but I'm pretty sure is a urethane based glue. If all you do is a single coat, even with rustoleum, you will run into the same issue and be worn down to shiny paint that didn't flock well.
Consider this, If you wanted to mix a bunch of fibers in your paint, it would strengthen and thicken the paint. That's what painting over the first coat is doing, then putting a second coat of flocking over that tends to give an even thicker coat fo flocking because of the increased volume of paint and drying time. I often will paint over the first coat, then set it aside while I do the next one to allow the paint to even out, it still has plenty of adhesion after five or ten minutes on that second dusting of flock and if you do it right, you'll notice not very much of the second coat flocking will blow off.
If you use flat rustoleum for your flocking glue you are going to have very very VERY spotty and weak adhesion. If you don't do a second coat, you will have a decoy surface that is not durable and you will be flocking it again with gloss the next time.
Why we hand paint white. For durability, for the ability to repaint easily. I usually touch up the white every two or three years. Secondly, white flocking is simply not white enough. Here are a few examples. Sometimes like on this wood duck head, I'll airbrush the white areas, while they seem fairly white, they aren't even close, so I hand paint over the area I airbrushed white. On large areas like the side of this goldeneye you can see the difference between the white flocking and the painted over flat white. The white area on the GE was flocked twice, white paint, white flocking and it's still not white/white. The most important color of flocking is black, the second most important color is white. The white surface painted over with flat still has the non glare surface, but it is much whiter than white flocking and won't stain as easily and can be repainted by anyone who can pick up a paint brush.
