Cyberpunk, steampunk, dieselpunk: why is it called "punk"?
Related but not helpful: Etymology of "punk"?
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The protagonists of cyberpunk stories are alienated, marginalised characters who are on the edges of society and are generally either professional criminals or at least not very law-abiding: They don't have a high opinion of respectable society, and respectable society doesn't have a high opinion of them.
This fits reasonably well with "punk", as does a tendency for them to hack things up in their own way rather than use (or be able to afford) whatever is the current off-the-shelf kit fit with punk's DIY aesthetic.
Cyberpunk has been summarised as "low-life characters in high-tech society" and "low-tech people in a high-tech world", both of which touch on this feature of the genre.
A story could have an influence of cyberpunk directly or indirectly through its influencing steampunk and dieselpunk and not feature such characters, though generally even if the protagonists of such characters are of a more privileged position they tend to be estranged from that position in some way.