Because the bats have 1000’s of Coronavirus strains it makes them useful . They have very long mRNA (30,000) and they don’t need nucleus to begin synthesis or replication.
Because ACE2 is a universally common receptor in humans, it is easy to get into the cell. Once introduced, the first 2 ORFs (open reading frames) are unique to COV / MERS / COV-2 .. the other ORFs differ slightly.
Vectors on an mRNA begin working with cell machinery immediately to synthesize proteins. HIV retrovirus DNA must go into nucleus and go thru several processes to unpack. If you can target a specific protein that the HIV virus needs .. and introduce a protein that doesn’t work correctly, then when HIV infected it can’t replicate or assemble or it replicate in the future — many approaches.
Expression of ACE2 receptors is interesting .. ACE can function on its own. Electron Transport Chain dependent on oxygen electrons is critical to life. Reducing ACE2 expression overtaxes the ACE function and body can’t down regulate innate immune response. So cytokine Storm happens in certain people. USA has high blood pressure problem — diet / processed foods. To the use of this virus to attack the world — appears to me — to have been intent on killing someone in each family (granny Sue, Uncle Jake, etc) and spread mass panic .. over whelm resources and force FEMA to bring in foreign assistance (China was clear on March) — only place to get assistance would have been China! Rest of world was busy.
Trump head faked China .. then crashed oil price.. giving them an honorable way out.. no Iran oil .. no sanctions violations with Iran or Venezuela .. no more support for Dem politicians .. in exchange cheap oil .. and we will help you with your ventilators (Beijing and Harbin) .. Save face. No WW3.
Rambling .. will end it here.