Because it would help with dividend reinvestment. If I understand correctly now I have to go and look for and add up security X dividends, then security A dividends and manually reinvest them.
It'd be easier to have a wallet for each, if you understand what I mean. Just reinvestment the amount that is available in the respective wallet.
Of course easiest would be if the whole process could be automated. And the cherry on top would be if partial share buys via dividend reinvestment would be possible.
It works in the "real world", don't see a reason why not with BTC.
Are fractional shares a real thing?
To do auto buys you would want to go to the order book no matter what? It's often pretty thin.