Does something in the bone meal make the calcium in the eggshells more bioavailable or is it just good practice because the bone meal and eggshells do their own thing without any help?
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.