For them it's about getting as much btc at the end of the day. Not btc held in altcoins, but btc to spend on the next altcoin
I prefer day trading also, even though I have to pay transaction fees, I feel safer when I have to buy an altcoin and sell it immediately if I have the profit. The situation of pump and dump is rampant in trading altcoin so we'll never know when they will pump or dump a certain altcoin so what I do is that when I see an altcoin that has a low price using Moving Average, I buy it and then calculate how much would be the breakeven price for that and then set my target price. Even if it's not so high, I will estimate that it will be hit after a few hours if I will be lucky and then when the target price is hit, I'll proceed to the next altcoin.