Why do translators send Xmas postcards or presents to their clients and colleagues?

First, it is a sign of politeness. And good manners make life in society more pleasant.
Second, it shows your clients and colleagues that you care for them. And that is really true: when I send my Xmas cards to my clients and colleagues, I always remember the good work we have done together and it is also a way for me to assess what we have reached together.
Third, it is also a way of doing soft marketing: you say thank you to your clients and colleagues for the work done. And you remember them that you are always available for more work to come in the future.
To all of you, to all the people who read my posts, I first want to thank you. And I want to wish you a Merry Xmas and a happy new year, from the bottom of my heart.