Loss aversion — the tendency to be more motivated to avoid a loss than to achieve an equivalent gain — shows up even in domains where every outcome is a gain of some kind, purely based on how the outcome is mentally categorized. A missed putt that costs a stroke relative to par (a bogey) is experienced as a loss; a made putt that gains a stroke relative to par (a birdie) is experienced as a gain — even though, from a tournament-scoring standpoint, one stroke is one stroke regardless of which side of par it falls on.
The fact that this shows up in elite professional performance, where every player has overwhelming incentive to make every putt, is what makes the finding so clean: this isn't a matter of insufficient motivation or skill, it's a demonstrated asymmetry in the underlying psychology of gains versus losses that persists even under maximum pressure and expertise.