My wife really likes Windows Phone and wanted a Lumia 1020 for the camera. I offered her my 6+ and she refused.

Trying to upgrade her to a new model is basically impossible. At the time we bought it if you went to any carrier store the Windows phones were clearly second class citizens with the best models not present. Carriers like T-Mobile wouldn't even sell you a decent model because they don't carry them at all and if you buy one separately you find that carrier specific stuff (tethering) is broken.

With Windows phone it was really like they weren't even trying to move units. Sure they built the software and hardware, but actual retail presence seemed pretty broken.

They also failed at continuity. There is no Lumia 1020 successor. The lineup in general seems fragmented with no regular predictable upgrade path and iteration.

AT&T did a pretty good job of promoting them a few years ago, but my problem is that I had a HTC Titan II, then moved up to a Nokia 1020, then when it's screen broke, moved up to a... oh wait. Exactly like you said, there was no upgrade path.

They didn't release any new phone models for something like 3 solid years. At the same time, the Nokia purchase removed HTC (who was at least somewhat enthusiastic about the OS previously) from the Windows Phone ecosystem.

So if you're a die-hard Windows Phone fan, they went 3 years with no new phones for you to buy! It's no wonder the OS is struggling. And while the Nokia 1020 is a fine phone, I loved, loved, loved my HTC WinPhone and it's a damn shame I'll never be able to buy that combination of hardware and software ever again.

The wireless carriers have the final say on which phones they stock and promote, not the manufacturer. There most likely weren't enough sales of Windows Phone devices to make it worthwhile for them to bother trying.

Carrier sales reps didn't like selling Windows Phones, and you can't blame them. From their perspective, they want to sell you a phone in the shortest amount of time that has the lowest probability of return.

Windows Phones had a different UI that meant the sales rep had to spend time showing how it worked, and even if he/she did make the sale, he faced the high risk of a Lumia getting returned because the customer found out some key app wasn't available on Windows Phone but was easily available on iOS and Android (their bank, or airline, Snapchat, and let's not forget Instagram wasn't there for a while)

(source: I'm a former Nokia employee)

Well penetration of WP is down yeah, but that only makes sense when Nokia Lumias immediately disappeared from shops upon announcement of the MS Lumia devices, and when MS did not market or promote those new devices very much. The 950 range was also largely unavailable due to stock levels. So for about two years there you couldn't buy a Lumia even if you wanted to. So it's not surprise that usage went down and that consumers weren't interested.

But my question is what was the corporate strategy? Did they see the success of the Lumia line and wanted control of it? If so, why did they immediately fire people and stop development of new devices?

It's so when they kill it there are fewer people to complain