Most of the users are investing their bitcoins in trading and that is the right thing to do, as only holding will not give you higher profits, as we never know what value bitcoin will hold in future.
Holding will give bitcoin users profit if even by any means, people will continously to accumulate coins at any possible way.
When people preferred to hold than to trade, make sure that they are adding coins on hold and not to hold only a fixed quantity of coins. Holding will just increase the value of the coins but the coins on hold will remain in numbers.