Because most people always think about the negative side first. 
It is normal because there is a mindset that "the more we wager, the higher chance we'll lose", and with this mindset most people think that there is no way for use to make profit by wagering more.
Lets use you case for an example, your starting bankroll was around $2k and you won $100 from the wagering contest.
From my perspective, it does not make senses for me if you are risking $2k just for a reward worth $100.
So I'm pretty sure you are wagering not for the wagering contest because if you are wagering for the prize only ($100), you wont start with $2k.


Preferences. Some of them may wager solely for the contest but some of them may not.