I dont Understand

 In McD:
1. Sauce - Why do people dispense tubs of tomato ketchup/chilli sauce, 

then only consume half of it? 

Or dispense a large splurge on the lid of burger box, only to dip a few fries in it?
2. Coke - Why do people ask for full cup refill, drink a sip then leave off? 
3. Table - Food and drinks is served on tray, and dustbins are provided in every corner of restaurant,

 but why don't people clean up the table after dining?

 They are able to self-service at the counter, but lets other do the cleaning after they eat?
4. McD Library - Why do people bring books to study in McD? 

Yes they have the rights to order a small coke and sit for 24 hours. 

If so, why don't we eat in the library?
5. Why do people bring stacks of extension plug, 

connect all to laptops, and turn the McD into a cybercafe?

And everyone sits there not talking to each other.

While it is not against the law, but don't these people know how to act and behave? I don't understand.