Human nature is such that it wants easy money. If you set up a business, it takes years to start making profit. Even if it is a startup, it might take time and one never knows that whether one will make money or not as 80% of new business or start ups close down within 2 to 4 years.
To be a fundamental investor, one needs to have a lot of money to invest and wait patiently for rewards. You get good rewards when markets are in a bull phase. When markets are in a bearish phase, one does not get rewards and one loses patience with the stocks he or she is holding and that time starts looking at short term movements.