It’s a good question, but asking it shows that the experiment was explained poorly.

The slits aren’t the reason you see an interference pattern. The slits function as two lenses, which, combined with the waves cause an interference pattern to appear on the wall.

All you need is some light in the same frequency, and something to bend it. That can be two slits, some glass, or an entire galaxy.

Of course, there are lots of conditions where you don’t get this pattern, but that’s more to do with the bars becoming too blurry to see clearly.