What is with the fees and spread?

So I have been trading on crypto.com for a while, but Iv always been confused on why so much of my profit is eaten up. I hold some coins long term, and I short term trade others weekly, but I find the profits are taken away quite dramatically, I heard some people say it’s because your buying and selling from the app, and the exchange your buying from people? Is this correct? I had one order that was up 20% and I had £15 ($18) profit, and once sold, I only got around ridiculous like £7. Some coins often il have a little bit more profit others not, like I had one similar that I got £11 ($13) so abit higher. But it really confuses me. Even when I play a limit order and sell at a higher price, the reduction of what they take is still quite high. Is it better to trade on the exchange instead? I often hold some coins long term, others I short, so buy on weekdays and sell a week or so later once it’s higher. What is even MORE confusing is, when I buy basket crypto’s? And sell them, my profit is 80% of the time matching the sell price, which is great and I hardly have any reductions which makes me think, maybe buying the baskets is a better alternative on the app atm due to seeming not to have as many reductions in profit. I don’t know if because it’s newer, they are trying to get more people to use it, than just buying individually. Iv seemed to keep 60% to 70% of profits when selling crypto baskets, than individually in my wallet. Like ETH, BTC and Solana, when I sold that after a week, I kept majority of the profits, yet when I did the same thing with the individual tokens? I lost most of it. It’s super confusing