Because it's one thing to feel like they reached into your pocket once, it's another thing for it to feel like they just want to keep it there constantly.
So, what would be better:
If a restaurant charged $per person, but it was unlimited all-you-can eat… You can have the lobster, steak, caviar.
Or, if a restaurant charged only for what you order— so the person who wants the lobster pays $50, the person who wants the steak pays $40, the person who wants the salad pays $20…. And the person who wants all 3 pays $110.
Breaking up pricing actually works to the benefit of the customer, more often than not.