great question. The alternative is not accepting 1000 applicants. Nobody said you have to keep up your job posting for two weeks, or two hours for that matter. stop once you have enough. Enough is defined by whatever number you would have filtered to. In the rare case none of the first ten applicants were appropriate, just open it again until youve got another tranche.
That's just another type of randomness (who was online during the short time the posting was opened).
You are assuming quality applicants are evenly distributed in terms of time of application - they aren’t. If you cut off at 100, you will only get a sample of people spewing fully automated application bots which mostly aren’t what you want.