Comment by close04
Mainly because they were introduced when the seats were set farther apart. Now companies squeeze more rows and keep the same seats.
But also because with any shared resource there's an expectation of decency involved. Some people just betray that expectation. They're the ones with the mentality that "they shouldn't have served alcohol if they didn't want me to get insufferably drunk", "they shouldn't have put the candy out if they didn't want me to take all of it", "why is the swing there in the park if not for my kids to use them continuously to the disappointment of other kids".
When your wife was pregnant someone probably let her go ahead in a queue, have her some priority for something, etc. That was a person with common sense and decency, not asking "why do queues exist", who doesn't do something only if there's a law about it.
I’m several inches over 6’ and if I don’t get a fire exit seat I’m highly likely to get seated behind someone who will call me “extremely rude” for wrangling uncomfortably and bumping their seat uncontrollably when they inevitably decide that extra 6 degrees of recline is worth more than my knee cartilage.