Our horse chestnut tree (which pretty much every year looks healthy)
never really puts out any chestnuts. Some years the tree is covered in
flowers, and other years not so much.

Last year there were lots of flowers, and lots of small chestnuts
forming, but most never got larger than a pea or marble-size before they
disappeared.

Is something missing from the soil? Fertilizer or something else?

Or are these trees know for being variable as far as chestnut production
goes?