Because it's not warm enough. This is the why an enclosure helps, a lot. If the air temp is not hot enough ABS will warp and not stick to the build plate.
Also you have to have an "all metal" or "bi-metal" hotend or the PTFE liner will detaeriorate rapidly causing the heatbreak to effective close up preventing filament movement.
Also it will emit really toxic fumes which can be deadly for any pet birds and not good for humans.
