Here's why:

* Anton van Leeuwenhoek, a Dutch scientist, is credited with the discovery of bacteria in the 17th century.

* He didn't use the complex compound microscopes of the time, but instead crafted his own single-lens microscopes. These were much simpler but incredibly powerful for their time, magnifying objects up to 200 times.

* He used these simple microscopes to observe pond water, scrapings from his teeth, and other materials, leading to his groundbreaking discovery of microscopic life.

While compound microscopes existed then, they were not as refined as Leeuwenhoek's simple microscopes, making them less useful for observing the minute details of bacteria.