Or because their kid or dog is in the car. Or because they have difficulty walking. Or because they just want to decompress and scroll their phone or listen to the news for 10 minutes. Or they hate crowds. Or they are immune compromised and don't want to be mingling with a bunch of people around a counter. Or they have social anxiety. Or they have a cold and just don't feel like getting out of their car. Or they are expecting a call from the baby sitter. Or they are having a fight with their spouse which they don't want to export into the public.
IMO, drive throughs are great, I hate crowds and queues (yes, the car line is a queue, you know what I mean), and it is much kinder to my bad discs in my back (transitions from sitting/standing is just murder, steady state is much better). It would take a egregious queue to get me to go in in most cases. But sure, I'm lazy or just reaaally bad at math. edit: I also find it hard to hear in high volume rooms with lots of reflections (like an in-n-out), and yes, the drive through can have it's own sonic issues, but it is generally smoother for me.
Sorry, but I get tired when people take the most uncharitable read, especially when they blanket apply it to everyone.