Is it the additional data you give them to enter the giveaway?

Basically. You’re telling TP-Link that you’re a business that’s interested in selling their products. In return, their Sales team now has your information and can pester you tell you all about the latest TP-Link products.

Additionally, they’re putting their products directly in the hands of customers who could become even bigger customers. If you, as a company, decide you like the product, then you’re probably going to buy more of said product.

Finally, TP-Link is being selective about who gets the freebie—they’re not just handing them out willy-nilly. From the fine print:

Offer valid only for SolutionX partners. One Insight S445 (2.8mm) camera per qualified SolutionX partner. Approval is required, and TP-Link reserves the right to verify applications

So there’s probably some sort of “legitimacy threshold” you have to clear in order to get the goodies.

Alternatively, check out Consent-O-Matic, which applies the most privacy-preserving features by default, and lets you choose more specific preferences. It’s also open-source.

You’re right. See my edit.

Report it to the FTC.

Edit: I named the wrong F agency. It looks like the FCC might be a better option: https://consumercomplaints.fcc.gov/hc/en-us/articles/115002234203-Unwanted-Calls-Texts-Phone