Please explain what determines the trading profits? Trading system cost?

The game almost every thing about the details. For example. Food Mining. Specified where it is taken, the points.

On Trade is nothing at all. And merchant ships do not like not animating. I would like to see the game better trade.

In general - you want to either zoom out to trade view or press space bar when you're zoomed into a system to see its "trade efficiency". You'll notice that the factors for increasing efficiency are there, but it's only a part of the puzzle.

Generally when you are picking your trade company headquarters you want to pick systems that have the luxuries that you want to use for system development. Utizilizing luxury boosting developments like Slag and Sludge, NPO's, certain pacifist buildings and  on your planets that have the luxuries you want not only increase the amount you get from the planet itself, but also increasing the output of your trade route.This was something that took me longest to learn. After you start utilizing this you'll finally find that you can use those tier 3 luxuries for system developments, rather than going the whole game without utilizing even tier 2 (like I used to).

This is most true, reseraching and building  Slag and Sludge is something I never bother to, but it probably top tier of planet specializations you can select. I guess I should finally learn to, as i prefer to ommit planet specializations altogether. ='(