Karika 17

सङ्घातपरार्थत्वात्त्रिगुणादिविपर्ययादधिष्ठानात्। पुरुषोऽस्ति भोक्तृभावात् कैवल्यार्थं प्रवृत्तेश्च ॥१७॥

The manifestation happens by the deformities of the three qualities, for the sake of, and supported by, the other. Hence, the Purusha exists as an enjoyer, driven by its tendencies, with the purpose of getting liberated.

The tendencies of the Purusha drives the manifestation. Hence, Purusha is the cause.