If you don't need components on the bottom side, it saves money to not do so. That means the board doesn't need to go through another pass on the SMT machine.
Even if a board is double-sided, it is common to avoid putting major ICs on both sides, unless the space constraints are severe. Often, people will only put passive components on the bottom side.
Even if a board is double-sided, it is common to avoid putting major ICs on both sides, unless the space constraints are severe. Often, people will only put passive components on the bottom side.