Getting back to Stephanie's original question about motivation of the lack thereof reminds me of some work I did many years ago with young children as a graduate student in child psychology. I was supporting a study in which the researcher was interested in what would happen if one identified an aspect of play that a child was passionate about and then provided the child with tangible reinforcement for engaging in that mode of play. As expected the amount of that type of play increased. Of course that wasn't the real research question that was being studied. What we really wanted to know is what would happen after external reinforcement was removed. When that occurred, the amount of time children spent "playing" at what they had initially been passionate about decreased significantly to a point far below what it had been before they received any external rewards for it. Providing an external incentive led children to experience a decrease in the intrinsic enjoyment (i.e., the motivation) they reported getting out of the activity. They were now doing it not for fun and their sheer enjoyment but rather to obtain an external reward.
So how does all of this relate to Stephanie's question? I think it brings out the difference between what we consider work and play. Work is typically thought to involve non-immediate/long-term/indirect return of gratification or satisfaction for oneself or others (e.g. wealth and health in long term, etc ). Play focuses much more on immediate/direct gratification that one gets from engaging in the activity itself (excitement, thrill, etc). Viewing work and play as entirely different activities is probably not terribly accurate as what is work for some can be play for others (whether or not one is being paid for the activity). A close friend of mine's work, for example, is as a pediatric surgeon. What does he do for "play?" He trims healthy trees and cuts down dead/diseased for his neighbors, friends, or anyone in the area who is aware of his form of play. Not what I would consider "play" but for Dr. Bob it brings about immense gratification. If an activity offers you both happiness while doing it (direct gratification) and also gratification in long term (indirect gratification) it can be both work and play at different times and in different contexts.
It's interesting that when people talk or write about what they do with their instruments some refer to "practicing" while others indicate that they are going to "play" their bass/guitar, etc. Personally, I find "practice" boring and have needed to train myself to view it as "playing" or "playing with" my bass. Thinking about it that way I look forward to engaging in the activity rather than dreading it. So to make a long story a little bit shorter, find the "play" in what you are doing whether that's moving into new musical genres, playing in a new band, playing with a new instrument, or taking lessons.
P.S. My son has, over the years, become an exceptional blues guitarist. Never took a lesson, never formally studied the craft (other than taking a course in the physics of music while in college which culminated with his building himself a mandolin), and of course he "never practices." Every time he picks up his guitar he just "plays it," "plays with it," or in GD terms "let's it play him." I think it's one of the reasons why whenever I see him outside of his job as a carpenter he's got a guitar in his hands.