The invulnerability orb applied to revives when it was implemented years ago. The developer team said they could not get it to only apply to spawns.
Additionally, the gate idea has been suggested numerous times. Justg stated that the team cannot implement the gate because it is too complicated of a coding process and the game would need an overhaul to make it like AL.
For anyone curious about this, I found Dolloway's explanation to be the most thorough. Sts simply cannot make a gate at the spawn point because of coding complications it would cause. I hope this helps answer anyone's questions about why this does not exist!