Sudras are majority 85% of society and they were Engineers, Metal Works, Potters, Carpenters, Artisans, Craftsmen, Tradesmen, Peasants, Weavers, Cart-builders and other Service Professions . If they stopped all works to build society and study Vedas how will society run? Study of each Veda takes 12 years with lots of restrictions on food, wealth etc. Its tiresome and time consuming and if majority society follows it then building of society shall stop.
Does this imply that Shudras are forbidden from the knowledge of Vedas? No!
Sudras are eligible to acquire knowledge from other sources like Agamas/Puranas and achieve the same end result. All such devotees are as respected as Bramhanas.
I envy no one, nor am I partial to anyone. I am equal to all. But
whoever renders service unto Me in devotion is a friend, is in Me, and
I am also a friend to him.(Gita 9.29)
O son of Prtha, those who take shelter in Me, though they be of lower
birth, women, vaiśyas and śūdras can attain the supreme
destination.(Gita 9.32)
Sufficient liberty of action is left to them in consequence of which
all individuals may attain to an equality of condition. (MB Anu CLXIV)
Yajnavalkya says By obtaining brahmajnana from a brahmana or kshatriya or vysya or shudra or even a person of low caste, person with faith should constantly practice the same.(MB Shanti 378,Shl 87)
I have already told you that people of all varnas can remain in their ashrama-dharmas and obtain jnana. Therefore, whether a person dedicated to jnana of any varna he will surely get moksha;this is the opinion of scholars.”(MB Shanti 378,Shl 91)
This is the procedure for the Diksha and its attending ceremonies meant for the Sudras. This is conducive to the deliverance from the worldly existence for all the four castes.(Varaha Purana 127.32)
They remain severally in their own Varna,Asrama and Acara,but are all impressed (without caste distinction) with the Cakra and Sankha which are sacraments of Vaishnava initiation.(Ishwara Samhita 7.179)
Yogis are born among all castes; and no caste-odium shall hold in their cases, for they have seen their souls.(Bharadvaja-Samhita 1.44)
Brahmins learned in the Vedas, monarch, regard a (virtuous) Sudra as equal to a Brahmin himself. I, however, O king, look upon such a Sudra as effulgent Vishnu of the universe, the foremost one in all the worlds.” (MB Shanti 302,Shl 12-18)
One who is a devotee of Supreme Personality of Godhead can never be called a Sudra, rather he is glorified as a Bhagavata or one who is connected with Bhagavan. If one is not a devotee of Lord Krsna,however,even if born of a Brahmana, Ksatriya or Vaisya family, he should be considered a Sudra. (Hari Bhakta Vilasa 10.165)
Trying to prove and recognize a Vaishnava devotee through his caste,form,place,home, profession etc is considered as the greatest of the sins. (Prajapathya Smriti)
If a devotee of Vishnu, even though he be a Chandala, is recollected, named, seen or touched accidentally by anybody, O dear madam, the former purifies them. (Varaha Purana 211.9)
It is through deep love that the Chandala makes me his own, while without it the Brahmin is nothing to me. (Garuda Purana 1.231.9)
A Bramhana who is expert in studying all four Vedas is not dear to Me. But a devotee who comes from a family of Chandalas is dear to Me. He should be offered gifts and one should accept gifts from him. He is as worshipable as I am. (Hari-Bhakta-Vilasa 10.127)