Plus - getting notified every time the card is used is a new thing and not necessarily something everyone has set up. Or, as mentioned above, the cardholder may not notice. Whereas trying to buy a big ticket item at Best Buy in front of their cash register security cameras and the card is already flagged - not the best move. That’s the reason for testing. You don’t get to try 5 or 10 cards until one works when you’re standing at the Best Buy cash register.
In the days before cellphones were everywhere (and before roaming was cheap) I flew into an airport and needed to call the shuttle to the car rental agency. I tried my credit card in the payphone (remember those?). The call did not work. Eventually I got change and called, but when I tried to rent the car my card was declined, I had to talk to the bank and get it straightened out first. Fortunately, they accepted my explanation of what happened; but they were watching for testing even back then.
I suppose when everyone has a notification on their phone for any card use, card checking will be less of a good idea. From OP and comments, I see we’re getting there. (Only one of my 4 cards notifies me…)