I originally got the card because of the initial points bonus and DL lounge access / priority pass but decided to keep it for a second year despite not even using it much. The 2 main reasons are:
1. Centurion lounge access - took a couple trips to vegas and the lounge was good. Now that they're opening one in SFO which I fly through twice a week, it'll save me from purchasing food or drinks at the airport.
2. Concierge - I'm a foodie and they've been able to secure hard to get reservations to restaurants. Having them try to get the reservations for me saves me time which I think is worse the annual fee by itself.
I use Chase Sapphire for restaurants and travel since I like the transfer partners better (Hyatt / United / Southwest) and SPG Amex for spg hotels since I primarily stay at SPG properties.
But if you don't value any of the benefits of the Platinum card then don't get it, it's as simple as that. It's like trying to understand why someone would ever buy an expensive watch or bag when you don't value those things.
I'm sure some people don't even care about any of the benefits and have the card because it says Platinum on it.