Attacks have become increasingly sophisticated, and often are invisible and undetectable by legacy security solutions. You read about these successful data breaches almost on a daily basis.
Security analysts do what they can with legacy tools, but these tend to swamp analysts with alerts that are difficult to understand and are often useless for rapid detection and remediation of advanced threats.
UEBA solutions employ a different approach by using variations of artificial intelligence and machine learning, advanced analytics, data enrichment, and data science to effectively combat advanced threats.
Read the white paper and understand:
The broad categories of security operations that UEBA can affect