That's not true; most Eastern religions are based either on deities or ancestor worship. Buddhism is arguably the sole exception.
It's also worth noting that Judaism, Christianity and Islam all originated in the Middle East and would therefore be considered eastern religions as well in terms of their origins.
Is ancestor worship really akin to theism, though? I'm not exceptionally well-educated on eastern 'religions' such as Confucianism and various Chinese traditional beliefs that practice it, but I wasn't aware there was the consideration of ancestors on the same level as gods. What Western scholars, influenced largely by Christian missionaries, historically and in some contexts presently refer to as 'ancestor worship' seems to me to be more about respecting our ancestors more than 'worshiping' them in the sense Christians may worship God.
Also, for the record, the term 'Eastern' religions, or Dharmic religions, is usually a blanket term used to refer to
religions originating in East Asia and the Indian subcontinent which are specifically separate from Abrahamic, or 'Western', religions, such as the three you mentioned. You can't just call them Eastern religions because of the Eurocentric terminology of the phrase 'Middle East'.