由于下面哪个原因，广告生态系统对机器学习技术的需求自 2017 年以来一直持续增长？

The correct answer accurately identifies the confluence of factors driving the increased demand for machine learning in the ad ecosystem. Heightened user expectations for relevant ads, coupled with evolving privacy regulations (like GDPR and CCPA) and technological shifts (such as browser restrictions on tracking), have significantly complicated campaign measurement. Machine learning offers sophisticated solutions to navigate these challenges, enabling more effective ad targeting and measurement in a privacy-conscious environment. While marketers using ML for pattern recognition and optimization, Chrome's cookie deprecation, and data scientists advancing ML are all relevant trends, they are either consequences or contributing factors within the broader context of user expectations and privacy changes impacting measurement.