Why are the Vedas called inferior in Upanishads?

The Upanishads are the philosophical departments of shruti. The Upanaishads are the Vedas. Nowhere in the Upanishads are the Vedas called inferior. It would be like calling yourself inferior.

Of course there is this statement in the Upanishad called the Gitopanishad. That Upanishad - Bhagavad Gita - is part of shmriti, though.

Krishna says:

Men of small knowledge are very much attached to the ?owery words of the Vedas, which recommend various fruitive activities for elevation to heavenly planets, resultant good birth, power, and so forth. Being desirous of sense grati?cation and opulent life, they say that there is nothing more than this. —Bg 2.42-43

In the minds of those who are too attached to sense enjoyment and material opulence, and who are bewildered by such things, the resolute determination for devotional service to the Supreme Lord does not take place. —Bg 2.44

The Vedas deal mainly with the subject of the three modes of material nature. O Arjuna, become transcendental to these three modes. Be free from all dualities and from all anxieties for gain and safety, and be established in the self. —Bg 2.45

All purposes served by a small well can at once be served by a great reservoir of water. Similarly, all the purposes of the Vedas can be served to one who knows the purpose behind them. —Bg 2.46

Srila Prabhupada explains:

The rituals and sacrifices mentioned in the karma-kanda division of the Vedic literature are meant to encourage gradual development of self-realization. And the purpose of self-realization is clearly stated in the Fifteenth Chapter of the Bhagavad-gita (15.15): the purpose of studying the Vedas is to know Lord Krishna, the primeval cause of everything.

So, self-realization means understanding Krishna and one's eternal relationship with Him. The relationship of the living entities with Krishna is also mentioned in the Fifteenth Chapter of Bhagavad-gita (15.7).

The living entities are parts and parcels of Krishna; therefore, revival of Krishna consciousness by the individual living entity is the highest perfectional stage of Vedic knowledge. This is confirmed in the Srimad-Bhagavatam (3.33.7) as follows:

"O my Lord, a person who is chanting Your holy name, although born of a low family like that of a chandala [dog-eater], is situated on the highest platform of self-realization. Such a person must have performed all kinds of penances and sacrifices according to Vedic rituals and studied the Vedic literatures many, many times after taking his bath in all the holy places of pilgrimage. Such a person is considered to be the best of the Aryan family."

So one must be intelligent enough to understand the purpose of the Vedas, without being attached to the rituals only, and must not desire to be elevated to the heavenly kingdoms for a better quality of sense gratification. It is not possible for the common man in this age to follow all the rules and regulations of the Vedic rituals, nor is it possible to study all of the Vedanta and the Upanisads thoroughly.

It requires much time, energy, knowledge and resources to execute the purposes of the Vedas. This is hardly possible in this age. The best purpose of Vedic culture is served, however, by chanting the holy name of the Lord, as recommended by Lord Chaitanya, the deliverer of all fallen souls.

When Lord Chaitanya was asked by a great Vedic scholar, Prakasananda Sarasvati, why He, the Lord, was chanting the holy name of the Lord like a sentimentalist instead of studying Vedanta philosophy, the Lord replied that His spiritual master had found Him to be a great fool and thus asked Him to chant the holy name of Lord Krishna.

He did so, and became ecstatic like a madman. In this Age of Kali, most of the population is foolish and not adequately educated to understand Vedanta philosophy; the best purpose of Vedanta philosophy is served by inoffensively chanting the holy name of the Lord. Vedanta is the last word in Vedic wisdom, and the author and knower of the Vedanta philosophy is Lord Krishna; and the highest Vedantist is the great soul who takes pleasure in chanting the holy name of the Lord. That is the ultimate purpose of all Vedic mysticism.