The Bone Meal provides Phosphorus for blooming and setting fruit, so I use it on tomatoes, peppers, eggplant, okra; just about anything that fruits. It’s cheap and effective!
The eggshells provide calcium to ward off Blossom End Rot, which is not a ‘disease’ but a lack of calcium. Calcium is the first thing to leach out of your soil (or anything potted) when there’s a LOT of rain - which is what we’re dealing with this season in Zone 4/5, in the SE corner of Wisconsin.
I use both Bone Meal and crushed up eggshells when planting out my peppers and zucchini, because they can get Blossom End Rot, too.
Thank you.