What Happened To Respect and Self Worth?

Why don't people value themselves enough to know they're worth more and don't have to settle? Why in 2014 are women and men still going after married people or people that are in relationships and even living with their mates? Why work so hard on making someone your own knowing he/she will never leave that person they've been with for over 20yrs? And if they do leave why don't people understand he/she will do you the same way...So my question is "What happened to respect and self worth?"