Having good manners is important to leading a successful social life, and to not be a sociopath. You say your amounts of "thanks" and "sorry" every single day. Yet, we don't usually think much about saying it. Have we been so used to saying these words (pressured by parents) that the words have become the default reaction to certain scenarios?
Everyone's been taught to say "please" and "thank you" by most parents. They tell you to say "sorry" when you have done something wrong, sometimes when it isn't even your fault, just to avoid conflicts. This isn't wrong in the slightest, but when you grow accustomed, and they come out almost literally at any slip of the tongue, you might not be really meaning what you say. This is what I mean by "Mannerism Deflation" - the phenomenon of saying "bless you" and whatnot increasingly, but the value behind the words decrease.
If you don't get it, think about real life dollar inflations, where more money is printed out, but the value of the gold stays the same.
If this goes on, the value of saying "thanks" and "sorry" will be worth nothing, and will be less genuine. We may have add "very" in front of the word "sorry" numerous times before the meaning is implied. This would in turn slowly prolong the brief interaction between you and stranger when you stepped on one's heel.
To stop this deflation from progressing further, we must think about what we are about to say. Stop using "sorry" as your default response when someone looks your way menacingly. Maybe, just maybe, we can slowly restore value to common mannerism phrases.