Well its only natural for people to be happy when they see their investment becoming somewhat successful.  When the price goes down, the long time investors won't really care too much about that as it definitely would be going up again but this price drops makes new investors happy as they get to buy btc or any other altcoin at lower price. So you can't really say that 'people' are happy when the price goes up as it includes both 1. The people who have invested in bitcoins since a long time and 2. The people who wanted to invest in btc and were waiting for the price to go down, the latter would be happy in this situation.