In the above circuit connection why switch is connected towards the negative terminal?

As answered previously...

The closed glass chamber of the bulb contains, an inactive (inert) gas, Argon. The glass chamber can’t be filled with air as the presence of oxygen will cause the filament to burn, i.e. react with oxygen. The glass chamber can’t be made vacuum. As in vacuum condition, the filament will evaporate because of very high temperature, making the bulb unusable. The only solution to these problems is an inert gas. The inert gas within the bulb will maintain a particular pressure, preventing the filament from evaporating. An obviously, inert gas won’t react with the filament. Nitrogen is also used like argon since it is unreactive.