The safe harbor provision of the DMCA exists entirely to take away power from copyright holders. It creates an entire class of businesses (internet service providers) who can't be sued for infringing copyrights if they follow certain rules. It makes copyright holders that abuse the provision pay both damages and legal fees of the victim. It enables the legal existence of sites like YouTube despite rampant copyright infringement.

Meanwhile, other provisions of the same act directly benefit copyright holders: prohibiting breaking of anti-circumvention measures, for example. This gives DRM its legal teeth beyond simple breach of contract.

How does this fit into your conspiracy theory? There isn't one single group that this act represents the interests of.

It isn't a conspiracy theory to say that media interests did the lobbying for DMCA. I cannot even find a reference to an ISP lobby that promoted it. Was there one?