Why do flight crew dim the cabin lights before take off?

The next two questions are actually more like complaints than questions…

When you are called to board your aircraft and they specify what rows of people are able to bored first – why do they let people on who are NOT in those rows?

When it is VERY clear how big your carry on baggage should be, why do they let people carry on stuff as big as a suitcase? The lady in the row behind me has just shoved a HUGE bag into the overhead luggage compartment. Her bag is so big there is no room for any other bags. SIX peoples’ carry on luggage is supposed to fit up there!!!

End of the complaints, I’m now sitting back mid flight enjoying a glass of wine, bagel bites and hummus. Aaaahhh fabulous.