Because, unfortunately, we live in a world of badly made things and what is worse, copies and knockoff of those few things which are made well. It is important that, when quality of manufacturing produces a groundbreaking instrument such as the strat or the tele, the genuine article be available and distinguishable from the copies of lesser quality.
Advertising helps people make wise purchasing decisions and distinguishes the real from the real copies.
I can say that the originals are rare and wonderful and somehow more than the sum of the parts. They make magic when played by the proper hand.
I have seen them make audiences weep, laugh and love but also and rage, hate and become violent.
People like Van Halen, Hendrix, Malmsteen or Cray, Clapton or Gibbons or Vai - they took the simple strat and changed parts of the world and powered movements and created magic that still sways masses.
What a thoughtful response, thank you!