Ironic, I know. I couldn't find where I originally heard this years ago, but the InternetArchiveBot page linked above says "InternetArchiveBot monitors every Wikimedia wiki for new outgoing links" which is probably referring to what I said.
I didn't know you can just ask IA to grab a page before their crawler gets to it. In that case yeah it would make sense for Wikipedia to ping them automatically.
Why would they need to own the archive at all? The archive.org infrastructure is built to do this work already. It's outside of WMF's remit to internally archive all of the data it has links to.