Answer:
because they have loads of work to do and they even have to bear some crazy patients so..
Couplet = couple = 2 lines
Quatrain = quadruple = 4 lines
Sestet = 6 lines
Octave = octagon = 8 lines
Thats how I try to remember it.
Shakespeare's sonnets are written predominately in a meter called iambic pentameter, a rhyme scheme in which each sonnet line consists of ten syllables.