The abrupt spread of Ganesha’s worship in Cambodia and Thailand around 550–600 CE was driven by a combination of cultural exchange, religious innovation, political developments, and changing social needs across South and Southeast Asia.

1. Cultural and Religious Exchange

During the 6th century, there was intense trade, migration, and cultural interaction between India and mainland Southeast Asia. This facilitated the awareness and adoption of Puranic Hindu deities—especially Ganesha—among Southeast Asian elites, priests, and artisans. Ganesha’s image and worship spread rapidly, appearing almost suddenly in temple art and inscriptions in Cambodia and Thailand.

2. Rise of Puranic Hinduism

Around this time, Puranic Hinduism was proliferating in India, with new temple-based traditions, rituals, and composite gods gaining prominence. Ganesha—now recognized as the son of Shiva and Parvati and as "Lord of Obstacles"—became increasingly central in religious rituals, often invoked at the start of ceremonies and undertakings. These new ideas were carried into Southeast Asia through texts, traders, and priests, and local courts eagerly incorporated them.

3. Political and Social Innovation

Southeast Asian rulers sought new spiritual legitimacy and symbols of royal power. Ganesha, who facilitated success, wisdom, and prosperity, fit perfectly with the ambitions of emerging kingdoms in Cambodia and Thailand. In Cambodia, he was even regarded as a major deity with the power to grant moksha (liberation)—a role typically reserved for Shiva or Vishnu in India. Temples dedicated exclusively to Ganesha emerged in Cambodia, highlighting his unique status in Khmer religious life at the time.

4. Distinct Regional Development

Unlike India, where Ganesha often remained a secondary god and was depicted in family or dancing scenes, in Cambodia and Thailand he was venerated as a primary deity and his worship was adapted to local contexts. Notably, the iconic mouse/rat vehicle associated with Ganesha in India was not adopted in Southeast Asia; forms of worship and depiction diverged sharply after initial contact.

5. Merchant and Artistic Influences

Ganesha was favored by merchants and artisans—groups playing crucial roles in expanding regional economies and inter-regional networks. These economic drivers further spread his popularity and secured his place in local iconography and rituals.

In summary:
Ganesha’s worship spread abruptly in Cambodia and Thailand around 550–600 CE due to dynamic cultural interactions, the rise of Puranic temple traditions, political innovation, and the appeal of Ganesha as a patron of success and remover of obstacles.

Once introduced, his veneration diverged from Indian models and rapidly became an integral part of Southeast Asian spiritual, political, and artistic life.