What are the fruits of righteousness?

Most of the nuts are this way. Pistachio, Almond, Walnut, etc. Nobody actually eats the fruit - just the seed. Mistletoe and Soapnut are also inedible.

Because a fruit holds seeds. It "fruits" (protects) them until the fruit's exterior has been used in some sort of way, and, the seeds are scattered.

If you mean why does " your fruit tree have no fruit " than it's either the tree requires another fruit tree to pollinate it or trees take time to mature before bearing fruits.

All fruits have some fructose, even puckery old persimmons and lemons.

yes