Purpose plastic screen protector inner screen

I bought a second-hand Samsung Galaxy Z Flip5 and noticed that the plastic film on the inner screen is no longer there. I know that from the factory, the inner screen comes with a plastic film already applied.

I asked the seller about this, and he told me that after a year it was removed in a store because the film was coming loose. However, no new one was applied afterward.

Does the film only serve to protect against scratches, or does this film have additional functions? Why else wouldn’t Samsung use this film on all their other devices (e.g. Samsung S25, etc.)?