> Isn’t sales tax only for consumers?

It depends how you defined “consumers”. If you mean “those who consume the good subject to the tax, rather than people who resell the good”, yes, ideally.

If you mean “not businesses” or “individuals but not corporations”, then, no.

> Ie companies reverse charge sales tax or omit it entirely.

Generally, the theory of sales taxes is that people (including corporations) pay sales tax on things they consume as a final good rather than use as an intermediate good in production or simply resell. The exact way in which that is determined varies somewhat between jurisdictions with sales taxes, but generally (assuming paper is subject to sales tax in a jurisdiction), if you are buying paper to print books that you sell, you don't pay sales tax, if you are buying paper to print internal documents that you use in running the business, you do pay sales tax.