Almost nothing supports HDMI Ethernet, it is the use of extra signal path on the cable to provide an ethernet link between two devices. Both devices have to support the extra signals and one of them has to be able to route, so it's basically someone's bright idea that barely has any support.

2) I've designed a system like this for a TV rental company, although legally a general retail TV manufacturer wouldn't want to do this because it causes reputational damage.

3) There's material cost for the modem and then there's a subscription cost for the connectivity. Either of which would reduce their profitability.

I spent a decade working in consumer electronics, working with all the major brands you know well, many of the white companies who make the components and the ODMs who make the boxes that will get a brand stamped on them by whoever is buying it.

Ultimately the TV business is barely profitable, most big brands sell TVs as something of a loss leader so that they can sustain their brand name. You spend each night with a Samsung, LG or Sony remote in hand looking at their product? Then they're winning in their eyes. Also because of the relatively high value of the TV it sustains their overall turnover without actually contributing to profitability. When a manufacturer launches a new TV they get about 8 months to make a profit on it, after that they're probably losing money because of downward pressure by retailers to drop the price. That's driven by consumer demand for cheaper rather than better products by the way, consumers have some responsibility for the state of the market.

The Smart apps systems cost the TV manufacturer, they have to supply the servers and infrastructure. They may make a small commission if a customer signs up to a streaming service on their device, but otherwise your general use of Smart technology costs them money every day.

Ultimately, most TV manufacturers have zero interest in spying on you. LG's biggest blunders can all be traced back to a lack of care and due diligence in their handling of data. Most of the time the 'mass data collection' is just accidental, someone in the development team thought it would be a good idea to collect data and some researcher is horrified by how much data gets sent back. Sometimes, someone gets the idea that viewing data could be used to put ads on the product, but ultimately they're not interested in what you watch, they're interested in grouping you into an advertising bucket so they can suggest you watch another movie with a Hemsworth in it.

I'm not saying that there shouldn't be oversight, and that these companies don't do stupid things for money, but ultimately there's never malice, or a desire to spy. Most of the overreach is incidental to the overall goal.

If someone doesn't want to use smart TV tech, then I'd advise them to not connect the TV to the network. There are set-top boxes out there that can do the job easily enough, and some of them might not even spy on you. One thing to remember is that many Android boxes you buy online, especially the "IPTV" ones, are riddled with malware. So don't think that by disabling Samsung and going to Kodi, you're making yourself safer.