It's in their nature
love to dwell in densly planted and shaded spots, they are also very lazy little buggers laying around most of the time. Mine do as well.. The first year i could only see them in the back corner of the tank under the echinodorus via the side panel. That was their home and rarely came out of that corner. Usualy they get more active when the lights slowely dimmed. While the tank slowly matured and the vegitation over all got denser through the tank they also migrate more often now and move from one spot to the other. But still after 2 years i more oftenly have to search to see them.
That's the big + with having a light controller able to simulate dawn, twillight and or full moon periodes at night. For the plants this isn't doing anything much i guess. But the fish will show much more natural display and more of themselfs during the day and night.