Those that can't dispose their altcoins and turn them into profit are holding it for their own purposes. Maybe the profit isn't enough for them to cover.
Or, they've got some other better plan that's being on its way as they hold it. But if you ask me, as long as you're happy and you're in profit, please do.
You might not see those opportunities to come again as the market is very different with altcoins than of Bitcoin.
I also suggest that if you have made a profit from an altcoin, whether it is 10 or 20 percent, then it is better for you to take the profit and not try to hold it any longer. The altcoin market is very risky and when the price has been pumped up there is a possibility that the price will fall again as has happened with the Manta project.
I've learned a lot from my past that as long as you're able to gain, reward yourself by taking it. The market is unpredictable and you'll never know when that time shall come to you and be rewarded again.
So, if the price falls and you sell at almost lesser profit or loss then it's your fault. And when that time comes, I'm sure that you'll get to learn that as well and won't become greedy anymore.
We have to get stomped before we learn things, right?