Right there, three steps to simply open your doors. Key fob, do absolutely nothing. For those like me that are in and out of the car 10 times a day, those three steps 10 times daily can get old. Key fob, walk-up, do nothing but simply open the door. No giving it a first thought, let alone a second thought. It simply just works and you never even think about it.
And not EVERYONE always has their phone with them. Again, I'm probably different than many since I use my car for work and am in and out 10+ times a day, but very commonly leave the phone in the car when getting out for just a few minutes or for an appointment as I feel it's rude for my phone to go off while on an appointment. They're paying me to be there, they deserve my undivided attention. So, phone stays in the car and I check the messages when I get back in. More notably, I don't have stop and take a phone out of my pocket, wait for it to wake, then tap on the screen to be able to open my doors. I walk up and skip all that and simply open the door. The key fob is so small and light, never even realize it's in my pocket. I do certainly notice when I have my 6x4 phone in my back pocket. Plus, having the app and bluetooth running all day runs down the phone battery much faster.
Again, to each is own. Whatever works best for each individual. At least there are options. With the Model S & X, they used to all be included, until Tesla cheaped out on the $120,000+ car to save $175. Actually, saves them even less considering they probably get them in mass quantity for $5.00 each.