I currently have 1 craft at 66, 2 crafts at 60, 3 at 40 and 3 at 20. These include mining, herbing and woodcutting (which I will always believe should NOT be included in crafting but it is what it is). So I indeed should also be able to level 1 more craft to 60 as well. But nobody's talking!
Where have I gone wrong and what do I do about it?
This is the crux of the matter. You can take all crafting and gathering to level 20. Then of those at level 20, you can advance only 6 of them to level 40. Once again, only 3 of those 6 can then go to 60. And finally only one of the final 3 can go to 80.
So in the end, you'll have 3 capped at 20, 3 at 40, 2 at 60, and 1 at 80 which as you stated above, is exactly what you have.
Planting is the odd one out, as it doesn't count towards these level caps, and can be raised to 80 regardless of the levels of your other skills.