Before we jump into the implications, let’s define what a license does for software. A license is a grant of rights. To use a piece of software, whether it’s open source or commercial, you need some grant of rights. In the U.S. and many other places, creative work (including software) is protected by exclusive copyright by default. This means that no one can legally use, copy, distribute, or modify that software without explicit permission from the creator/author. This permission comes in the form of a license that grants the right to do so. Without that license, the baseline assumption is that you do not have permission to use the software.
Clearly, including an open source component without a license in a commercial application can be problematic for a company. Organizations that use unlicensed code are at a greater risk of violating copyright law than those using licensed components, because in the absence of a license grant, a user can’t determine what their rights are (if any).