Simply put, the security reason is to keep the Delegacy in trusted hands, and logistically the Delegacy being a non-political role doesn't really intrude on what Shareholders and the Managing Director want to do.
There might be a day when we decide on some structure to elect the CEO, though that day might not come either as the Delegacy has been held by reasonable folks so far.
Though in my experience of Delegates of the CU and HRL, there were only ever a small number of active Delegates elected i.e. Harmoneia, Loftegen, myself, Altmoras, and Funkadelia, were the most active as I remember. The rest tended to fall into inactivity before even finishing their term. So there is an argument to be made that Delegate elections in sinkers doesn't really deliver much of a benefit vs Delegate succession.
That said, if we were ever to do Delegate elections in the distant future, it would be best to vet candidates on security grounds and put in activity requirements, than have the heavily open and easily subverted elections the HRL* and CU* regimes had.
Hope that answers your question.
*Humane Republic of Lazarus and the Celestial Union were highly Democratic regimes of past Lazarus, which held Delegate elections every 4 months roughly.