You are right, it is possible it just takes a lot of insight and effort. I cannot speak for the other teams, but as a person on your list I can only explain how I got the money to start trading.
1) In my startup team was a player that I sold for 200k ish
(2573737).
2) I made a spreadsheet calculating which combination of skills would be best for my team and thus most profitable.
3)I found out that you can buy players on weekdays for half the price you pay for them in weekends
4)I observed the market for a few weeks while making enough money on selling trained players e.g.
(2347489) and thus keeping at least 200k in stock.
5) After I understood the market, I started buying improvements to my team and sold of my old team members for a profit using minimum prices.
I don't know if there was anyone who wanted to know how it worked, but just in case, this is how i became daytrader.
Now I mainly trade to cover my weekly costs as I'm not even close to filling my stadium and the 70k+40k a week in salaries does a lot of damage to your budget.
Hope it gave you all some insight,
Happy holidays,
Floppzzy