Question

why doesn't food entre the trachea instead the oesophagus

Answer 1

Because epiglotis in the throat prevents the entry of food into the trachea

Answer 2

Food does not enter the ‘trachea’ instead of oesophagus during eating because the trachea or the windpipe is covered by a flap known as epiglottis.

Epiglottis is look like a leaf-shaped, stiff but elastic, cartilaginous flap covered with a mucous membrane that is attached to the top of the ‘larynx’, behind the tongue.  

During food intake, the epiglottis closes the tracheal opening and prevents food to be accidentally swallowed into the windpipe and lungs.