You could create an Automated Action to change this behavior.

Activate Developer Mode and visit the Technical --> Automation --> Automated Actions (if this menu isn't present, please install the Automated Action rules (base_automation) module.

Create a new Automated Action:

Code for you to copy/paste:

# if this is a Receipt with a Source (possibly automatically made)
if record.picking_type_id.code == 'incoming' and record.origin:  
  # find the PO that made the Receipt  
  located_po = env['purchase.order'].search([('name','=',record.origin)])  
  # Remove existing followers   
  for follower in record.message_follower_ids:    
    record.message_unsubscribe([follower.partner_id.id])  
  # Add the same followers as the PO  
  for follower in located_po.message_follower_ids:    
    record.message_subscribe([follower.partner_id.id])

This will:

• Check that the newly created Receipt is in fact a Receipt, and wasn't created manually.

• Find the PO that created it

• Remove all followers from the Receipt

• Add the same followers from the PO to the Receipt

Note:  If there are no Followers on the PO, there will also be no Followers on the Receipt.