Much as one answer is 'that's the way it's always been in Elite'. I suppose another, better, one is there are so many ways to use trade data it isn't worth storing all the information (or working out how much access they need to be able to give) per player in any meaningful way. And working out profits likewise, do you need point-to-point, would you prefer point-to-spread, max profit across a range of systems?
For instance I started off noting everything and built a spreadsheet to deal with the maths but now i have a Type 6 that's uneconomic as I don't need the cheap or low margin items and frankly it's a bit tedious. I've moved onto a database and am changing the info I gather. I've taken a break from trading to work out how i want to deal with it in the larger capacity ships.
Some people will only want to note items as high, medium, low. Some won't care at all.
I've never found external tools from paper to spreadsheets to be immersion breaking, that's just another part of the cockpit that you can't see in the game.
