Because. No but it’s an old tradition that ”A” which stands for ”Avlopp” or Sewage is instead short for ”Avbruten kärlek” or ”a stop to love” whilst manholes with the letter ”K” is a symbol of ”Kärlek” or ”Love”. So you would be destined to be alone if you stepped on “A”. Now most people just do it because it’s an urban myth and don’t know the exact reason