In The Rebel, Camus asserts that
Progress, the future of science, the cult of technology and of production, are bourgeois myths, ...
Why is Camus defining these themes as "bourgeois myths"?
In this chapter, Camus is comparing "the Christian and Marxist world," and finds that the two have much more in common with each other than either does with the "ancient world" – by which he largely means Aristotelian Greece. "For the Christian, as for the Marxist, nature must be subdued;" he writes. It may help to understand if we restore the full text of the quoted sentence:
Progress, the future of science, the cult of technology and of production, are bourgeois myths, which in the nineteenth century became dogma.
In defending this view, Camus refers to Renan's "Future of Science" - which he says
gives the most accurate idea of the almost mystic hopes aroused in the nineteenth century by the expansion of industry and the surprising progress made by science.
Camus argues that "this hope is the hope of bourgeois society itself" because bourgeois society is
the final beneficiary of technical progress…[w]hen we are assured that tomorrow, in the natural order of events, will be better than today, we can enjoy ourselves in peace. Progress, paradoxically, can be used to justify conservatism. A draft drawn on confidence in the future, it allows the master to have a clear conscience. The slave and those whose present life is miserable and who can find no consolation in the heavens are assured that at least the future belongs to them. The future is the only kind of property that the masters willingly concede to the slaves.
Both Marx and Hegel, Camus states
continued on the path of nineteenth-century bourgeois thought…that: "The gradual and progressive development of equality is both the past and the future of the history of man."
Perhaps another part of the question may be rooted in the definition of the word "myth." In modern times, many take it as the second definition used here
[a] person or thing existing only in imagination, or whose actual existence is not verifiable.
However, if we instead read the use of the word myth here to lean toward the first definition
a story…[which embodies] a belief…in which often the forces of nature and of the soul are personified.
we might better be able to understand Camus' point. Or, as a more recent touchstone might phrase it:
On this immediate level of life and structure, myths offer life models. But the models have to be appropriate to the time in which you are living, and our time has changed so fast that what was proper fifty years ago is not proper today.