I see that people support that altcoin suits better for day trading, and not for holding. I just don't get why.
Where did you get this information? Altcoins are suitable for both day trading and long-term holding. It all depends on the tasks that you set for yourself. If you have a financial cushion for the next couple of months, you can easily store your savings and not worry about price spikes in the market. Storage is not for the faint of heart)