Why do we need a chain of resistors to increase the voltage?
It's an SMT practice board. ALL of the resistors are 10k, probably because whoever's running the course didn't want to have to stock different values. Therefore, to get a value of 30k, they put three in series.

Sometimes, multiple SMT resistors are put in series for high-voltage circuits because their individual voltage ratings are insufficient. But that isn't an issue in a circuit that outputs 5.5V at most.

BTW, before you reflow the board, you should flip over the resistors that are showing the white side up. It makes no difference functionally, but it makes it easier to inspect the board afterward.