From the editor's post a few days ago, it sounds like there's always been that contingent of submitters who very clearly think that any combination of words put together on a page should be accepted for publication (he talks about rejecting obviously plagiarized stories, only for the submitter to come back with, "But I need the money!"). AI has just given those people a tool to inundate the market and waste even more of the editor's time.
To me, this sub window closure feels more like the magazine needing some time to regroup, come up with a plan of action, and execute. The editor talked about how they're already blocking the IP addresses of people who submit AI stories, and may have to reject submissions from people using VPNs/hiding their IP addresses.
Sidenote: I wonder if this particular flooding of Clarkesworld (the glut of AI submissions in February nearly tripled those in January) impacted the quality of the most recent Clarkesworld, which, as I read from Bick's review, contained a story that used the word "smoothened" multiple times and another story that said cancer had gone into remission when it was the opposite.