The answer is that they do indeed flower, but it is rare and only when they grow to maturity. Which requires the following conditions.
As a houseplant, Pothos remains in its juvenile phase with smaller foliage, concentrating its energy on the vegetative growth of leaves, stems, and roots. Under these conditions, it will grow beautifully, but will never get the chance to flower.
Like other members of the Arum family, Pothos flowers consist of a spathe and spadix. The spathe is a cream and purple, concave structure behind the upright spike-like spadix.
If you live in USDA zones 10-12 and grow your Pothos in a tropical greenhouse or climbing a tree outdoors, it may possibly flower. Indoors, however, It will thrive in its familiar juvenile phase of growth when given the right growing conditions.