"You don't know what you got 'til it's gone" is an idiomatic variation on the original phrase that has mostly worked its way into the vernacular, more than anything, as a consequence of Joni Mitchell's 70's environmentalist anthem Big Yellow Taxi. The context of its usage in that song makes the "only" pretty obvious. And I would argue that it might even be implicit even without said context, just by the sentence structure, but obviously mileage will vary with regard to the semantics.It's probably a different way of saying "you don't know what you have until it's gone"
Just as a pedantic note the full quote is "You only realize what you have once it's gone"
The "only" adds all the meaning. Sorry if I'm coming off as a bit of pedantic twat
Anyway, the worst offender is the voice that literally says thank you during a CE. WHY IS THAT EVEN A VOICE LINE?!