The question is not the division of labour; after all it takes several kinds of skills to build a house - say an architect and a builder; but the atomisation of labour in factories where very small and discrete tasks are set. Thus reducing 'artisans' to mere tools.
This is just one dimension to the notion of alienation.
This idea, which may seem 'Marxist' in orientation was actually introduced by Adam Smith who wrote in his Wealth of Nations:
"The man whose whole life is spent in performing a few simple operations, of which the effects are perhaps always the same, or very nearly the same, has no occasion to exert his understanding or to exercise his invention in finding out expedients for removing difficulties which never occur. He naturally loses, therefore, the habit of such exertion, and generally becomes as stupid and ignorant as it is possible for a human creature to become.
The torpor of his mind renders him not only incapable of relishing or bearing a part in any rational conversation, but of conceiving any generous, noble, or tender sentiment, and consequently of forming any just judgement concerning many even of the ordinary duties of private life...
But in every improved and civilized society this is the state into which the labouring poor, that is, the great body of the people, must necessarily fall, unless government takes some pains to prevent it."
and echoed by Marx:
Marx argued that increasing the specialization may also lead to workers with poorer overall skills and a lack of enthusiasm for their work. He described the process as alienation: workers become more and more specialized and work becomes repetitive, eventually leading to complete alienation from the process of production. The worker then becomes "depressed spiritually and physically to the condition of a machine".
It was here that the concept of alienation was isolated; but this is only one dimension of said concept.
For Simone Weil, a Marxist intrellectuel who worked in a French factory for three months she discovered that a factory creates:
"une docilité de bête de somme résignée"
("the docility of a resigned beast of burden").
and she had also written in her notebooks that the speed itself of factory work deadens the soul, whilst orders that one have to accept deaden consciousness.