A recent study from the California Permanente Medical Group confirms this fact. They studied 131 adults from age 18 to 82 who had a first-time shoulder dislocation. Looking back over five years of data collected on this group did not offer any conclusive predictive factors.
Younger patients involved in contact or collision sports were more likely to dislocate the shoulder a second time. Likewise, younger patients whose jobs required lifting the arms overhead were at greater risk of re-dislocation. But not everyone in this group did suffer a second dislocation.
Why did some dislocate again and others didn't? We don't know. Analysis of all the data collected never identified any specific factors to predict the outcome. That being the case, the authors of the study did not see a need to push for surgery early on.