Just saw this last night. At first, I was disappointed, expecting more of the creatures. But, afterwards, as I thought about it, I realized that the Title of the movie was "DAY ONE"...this was just the beginning of the aliens attack. So, we all know, from the first and second installments, that they don't leave or get defeated...they are "here to stay" and do much more damage.
The defeat of the aliens, as we all know, come in the 2nd installment "A Quiet Place Part II" and that the original, "A Quiet Place" was not the beginning, but an intermediary step in their invasion. So the true sequence should read (1) "A Quiet Place: Day One", (2) "A Quiet Place" and finally, (3) " A Quiet Place Part II".