Thomas, I too am an amateur, and have the lofty goal of the US Senior Am in four years. I have taken my handicap down from 10 in 2011 to its current 4.9; trying to get to scratch in the next 4 years, only so that I can hopefully get through local qualifying. I realize that I have aspects of my game that need improvement.
I know that I am just playing mental games with myself over the semantics I use to describe what I do at the range, but it works for me, but it reflects the motivation for many people that love the game - such as the people on this site. So, to achieve my US Senior Am goal, the key for me is to "go play more games" in the areas that need personal improvement.
I once "shared my thoughts" (not "gave a speech") about the impact of using words to describe people and actions to a room full of people. For example, am I a "father" to my children or their "mentor?"
Bringing this full circle to the point of the thread, about why golfers practice, I would answer it this way: some golfers may practice, but people that play golf - which is most of the people on this website - do so in a variety of ways. As a person who frequents this site, such as yourself, I don't know if you recall the thread a few years ago about your most memorable round. Almost none of the responses had anything to do with scoring; it was who was in the foursome, the course, etc. My point is that a person who loves golf doesn't practice; a lover of golf plays the game of golf wherever and whenever the opportunity affords them the chance to play. Any benefit derived therefrom, such as a lower score when on a course, is just a side effect of getting to play a game we love. Cheers.