linear-gradient() background doesn't work for <option> tag of non-multiple <select>

Question

While at the same time for the ones of <select multiple> it works fine.

Why?

option {
   background-image: linear-gradient(to top, white, pink);
}

<select>
  <option>one</option>
  <option>two</option>
  <option>three</option>
</select>

<select multiple size="3">
  <option>four</option>
  <option>five</option>
  <option>six</option>
</select>

P.S. Stackoverflow makes me to add more text for explanation. I guess the case is clear enough already.