Because you are charmed by the power and beauty of language as employed by masters of the literary arts—storytellers, poets, playwrights, and essayists.
Because you want to experience a wider, richer range of such writing, learning better how to enjoy and appreciate its intricacies and its subtleties.
Because you hope to assimilate into your own writing and speaking some of those masterful techniques, if only by osmosis, but also by explicit imitation.
While you may not aspire to literary artistry and published authorship, you do want to write with style, grace and felicity. You want to possess a copious vocabulary and know numerous syntactical forms for expressing yourself impressively.
Only as you immerse yourself in the best of literature will you absorb its methods. Even more palpably than sight reading does, reading literature aloud impresses its sonorities and patterns of rhetoric on your pulse and your memory.
If you wish to be a wordsmith, attend ardently to the greats and emulate their ways.