I feel this is typical for a newcomer to the business- lower commission rates on most sites until you reach a sales amount. I had the same feeling as you- are my photo just of lower quality than that of others? I have come to realize that my quality and type of photos (high demand) had to improve thus after two years I am around $.92 a sale. Also make sure you place photos on MS sites that tend to payout high prices (i.e. , Alamy, Pond5) - you will not get a lot of sales on the higher payouts but they are nice when they happen and sure boost your Revenue Per Download (RPD) ratio.
The take away- don't worry too much right now just learn what is in demand and always seek to improve your quality via lighting, composition, key wording and photo editing.
Good luck...
T