That takes effort, which is its own cost.

I -could- go back and forth 30 times and end up with a satisfaction-maximizing plate.

But I'm not gonna do that. I'm going to stack some lettuce because I know it's a good base for whatever I get next (though cheap for the restaurant). I'm going to pick a quantity that leaves room for unexpected yummies ahead out of sight, but also is sufficient that if I find few things I like ahead I'll still be happy with my salad.

I don't even manage to maximize the outcome at buffets that I've been at before with mostly static contents.