Here's why:

* We've only discovered a small fraction of planets: We've found thousands of exoplanets, but this is a tiny fraction of the estimated number of stars in the Milky Way alone.

* Planets are diverse: The planets we've found come in a variety of sizes, compositions, and orbital configurations. Some planets may be too small, too close to their star, or too far away to be detectable with current technology.

* Star formation is chaotic: The process of forming stars and planets can be highly variable. Some stars might not form planets at all due to the specific conditions during their formation.

However, evidence suggests that planets are common:

* Statistical analysis: Studies based on exoplanet discoveries and the way stars form indicate that planets are likely the norm, rather than the exception.

* Observations: Telescopes are becoming more sensitive, allowing us to find smaller, fainter planets and even protoplanetary disks (the building blocks of planets).

In conclusion:

While we haven't found planets around every star, the evidence suggests that planets are likely common. However, we are still in the early stages of exploring the vastness of the universe. It's likely that future discoveries will continue to refine our understanding of planet formation and the prevalence of planetary systems.