The sequence up to «مَالِكِ يَوْمِ الدِّينِ» is praise and description. «إِيَّاكَ نَعْبُدُ» introduces an immediate sense of devotional address. The shift is more significant than simply refreshing the listener’s ear.
مَالِكِ يَوْمِ الدِّينِ إِيَّاكَ نَعْبُدُ
Master of the Day of Recompense; You alone we worship.
The movement from praise to supplication corresponds to a worshipper recognizing divine attributes and then expressing worship directly. The change therefore serves the content of the utterance itself.