Great question, yes it is ultimately your low steem power. For more technical information you will need to learn how the reward pool works.
Basically there are only so many new coins made each week and more posts combined with lower price for steem lead to rewards going down.
At a certain threshold the steem network deems a reward "dust" and rounds it down to 0 which leads to no payout.
Take a look at your profile: https://shadowbot.us/shadowbot/dashboard.php?shadow_id=413
The last vote you cast from shadowbot:
Permalink VP Shadow Reward Voted
@mykos/mykos-coin-selling 100% 0.00209848 SBD 2 hours ago
you see 0.002 SBD was the entire reward, and curators only earn 25% of that, which would be 0.0005 SBD (dust and rounded to 0).
The best thing to do is while Steem (Power) is under $1 stock up as much as you can and always use 100% power up for your posts to continue to grow that SP! Around 500 SP you should never run into these issues!
Hope that helps a little!
Awesome, you will notice at ~500 SP you also get the Voting Power Slider as well which is super nice for allocating less than a full 2% each vote you cast manually!