Could be the state of the system restricting the access to high-paying missions. Is it a big system that has multiple stations/outposts? I would check around them and find whichever is the biggest to base yourself out of there, see if you have more success at those locations.
Also keep in mind that some of the higher-paying missions might have higher requirements - cargo space, etc. So make sure you check your Inventory; you need enough room to accept mission rewards (if it gives 4 commodities as a reward and you have no cargo space, it won't show as available). Also check to make sure you've got room for Data and Materials, too.
Another factor is the economy of the system; if it's, say, an Extraction system, and you're not into mining, then there won't really be much work for you to choose from. If you're looking for hauling missions, high tech, industrial, and agricultural are all good systems. I personally prefer high tech systems - I made my first home in a high-population high tech system.
If you're really looking for a system with a lot of trade, you can use the galaxy map to show trade routes, and pick one out that's a high-traffic system. The galaxy map can filter a lot of these bits for you - you can just show high tech, high population systems, or just agriculture systems, etc.