Why 'Hiding the Truth'?  (You are referring to the adage/maxim as a whole.)

Why is this pithy description used as a metaphor in human relations? It think it is because hiding the truth is like sweeping dirt under carpet. (This is the long, formal idea presentation format.  Your short style is good for aesthetic and artistic uses such as poetry, adornment, or jingles.)

No matter how long it's (in) hiding, it stinks!  (GREAT WRITING IN ENGLISH!)

Why would someone hide the truth?

Hiding the truth is like sweeping dirt underneath the carpet. No matter how long its been hiding, the truth is still there.

Good job illustrating your thoughts with similes. I choose to correct by adding "the truth" and taking out the word "stinks" because I felt it is irrelevant to "dirt".