I had a lab in MySQL, and back then, the only option to develop in Windows was MySQL Workbench, which was as heavy as it got. Running an SQL statement was painfully slow, and iteration cycles were huge.
In Linux, you would write your SQL in Kate, and run MySQL's cli in the embedded terminal. Once ready, you would click the button “pipe to terminal". Instant run. What took many minutes in Windows took less than 2 seconds in Linux. How can you not love this?
Another reason was Amarok, an (the) mp3 player. Do you like how Spotify and other providers create automatically infinite playlists, radios, etc based on your tastes? Yes, KDE had this since 2002 I think? It was first copied by iTunes, then by Spotify, and now is considered a standard function. :)