a more powerful one (120 W), but it becomes hot all the same.
The rating of a transistor is how much it will take before it is damaged. This is not related to how hot it will get when you pass a certain current through it. That is fixed by the circuit you are using it in. If you have 1700mA through a transistor with a saturated on voltage of 1V then you are going to have to burn 1.7W of power in the transistor. This is the same amount of heat irrespective of what transistor you have.
Yes a heat sink is the way to go if you are within the current rating of the transistor.
they all were using usual bipolar transistor, I don't know why.
Transistors were around before FETs and so were cheaper and more widely used. They can also be switched with smaller voltages / currents. Typically a FET will need 10V to turn it on but now there are logic FETs that turn on at 4.5V but logic FETs that handle higher current are not so common.