Actually, it's not even close. 10,000 attempts to guess a 4-digit number are certain to succeed. 100 attempts to guess 100 4-digit numbers have a good chance of resulting in no hits. For each 4-digit number, you produce 100 different guesses (with no repeated guesses for that number, because that would be silly). There's a 100/10,000 chance of a hit, and 9,900/10,000 chance of a miss. The chance of missing on all 100 4-digit numbers is (9,900/10,000)^100 = 0.366 = 36.6%. That's substantial!

Guessing 100 numbers, there's a chance to produce 2 or more hits, of course.

But that means you have pretty low conversion rate. You have 1000 numbers of stolen cards, and you only going to get 10 of them? It reduces profitability substantially. And even 100 attempts is enough to mark card as stolen if bank is watching it.