Why that Wall clause? Why not just call it unblockable?
(Back in the day, rules existed to the effect that creatures with the subtype Wall had the defender ability built-in. This rules baggage doesn’t exist today, and older wall cards have had defender added to their Oracle text. Click through the printings of Wall of Roots to see the difference.)
Sure, Carnivorous Plant had the drawback of not being able to attack. But if you controlled one, you were better prepared for a Thicket Basilisk, or an attacker enchanted with Coils of the Medusa, or even the Siren's Call of an Invisibility Nettling Imp.
Still, walls mattered in those days thanks to those snippets of text. Defenders still matter today, just with the more flavor-flexible defender keyword, as seen on Wakestone Gargoyle or Slithering Shade.
Just beware of the Tower of Coireall.