Scenario: you are driving in the smart lane: tyre blows out or engine seizes, and car rapidly becomes immobile. What are the chances then of a pile-up? Nowhere to go, and emergency services don't yet know there is a problem, so no red X over the smart lane.
Many years ago, my husband DID have a blowout on a stretch of the M6 in Lancs that has no hard shoulder. Scariest thing ever! Only saved by the fact that it wasn't at its busiest then.