One of them is the expectation of huge increases in value, resulting from the fixed cap and the assumption that it would replace other means of payment. That turned bitcoin into an allegedly safe and lucrative investment, and a speculation tool. Most of the big problems that bitcoin is facing today are a consequence of that undue retargeting of the project.
Again, economics, Professor. "Hoarders" is just a disparaging term for savers. Any economy needs savings for capital formation. If the very first cave man hadn't deferred consumption in order to have time to to make a spear that would make him a more efficient hunter, we'd all still be living in trees.