1. You do realize that, even if this price drop hadn't occurred, your ATV3's would have dropped in value the moment the ATV4 came out, right?
Therefore this price drop does not impact you any differently than if Apple had simply released new hardware instead of doing the price drop. Because either way: when the ATV4 came out, you would sell the old ones for a lower value than what you paid for them.
2. Can you point out one product (apple or otherwise) that is worth the same amount of resell value 3 years later?
3. Hopefully you at least understand why Apple did this. When Apple TV 2 came out in 2010, it's only competition was Roku, which was very close in price-point. Today, 5 years later, there is a lot more competition (Roku has dropped its prices significantly, Chromecast now exists, FireTV now exists) all for far lower cost than Apple TV's $99 price point. For Apple TV to maintain it's lead, Apple decided to drop the price so it's less difficult for people to justify buying one, AND they announced the HBO Now 3-month exclusivity to try and sell a lot of them over the next 3 months. To me, this demonstrates that Apple finally regards this as more than a "Hobby", since they are making efforts to stay competitive in the game.
----------
Refurb Apple TVs have been "sold out" intermittently over the past 4 years. The present-day sell-out may be due to the price drop (from $75 to $59 for the refurb), but them selling out is not unprecedented. I expect there will be refurbs available soon.