Players need to be more observant
Indeed. Illegal decks were much less of a problem when players moderated themselves rather than only Staff doing it. Autonomous moderating will always be the most efficient form and accounts for 98% of moderating being done (you, the user, thinking twice before posting that post that was just a bit too personal).
That's MY reason for removing the deck check rule. A philosophical principle that can result in better overall awareness.
The general TO reason is, of course, to reduce the work load, which has become necessary.
However, there is a middle path we can take. We can allow deck checks to be requested by both players and TO's alike. This means the TO can demand it when they have time to spare, but do not HAVE to delay other duties and thus the next round because they HAVE to check decks. Similarly, users can request deck checks by both the TO and other users (as they always have been able to do, just have chosen not to).
In the end, you're older players arguing for something you've always had access to and shouldn't need, but for new players I'm perfectly willing to add a clause that simply explains that deck checking is a thing you can do.