Could the causal chain go the other way? (Nobody shipped any devices with that architecture, because app availability was too low)

It's possible, but I think the more likely issue is nobody shipped very many devices with x86, because Intel cancelled development of x86 for phones[1] before they had many design wins.

Also, and I missed this at the time, it seems like Qualcomm was restricting manufacturers from also using competitors chips[2], although it seems the ruling was reversed on appeal [3], there's still evidence of restrictions. It would be unappealing to market an x86 device if it means losing access to Qualcomm cpus, especially in an era where Qualcomm modems were practically mandatory, so it makes sense that the only x86 (Asus Zenphone) I can think of is made by a company that didn't make a lot of phones.

Personally, I don't think the lack of app support would have been that much of a problem for sales of phones in the 2012 to 2016 time frame. If you got a couple hundred thousand phones out there, app developers would add support, because it wasn't too hard, a lot of developers were running x86 Android emulators, and they may have already had the x86 native code libraries and just didn't ship them because why bother when there's no phones.

Some of the first generation Asus Zenphone ran on x86, and it might have been rough for a while, but I think they sold reasonable numbers, and app developers started shipping x86 libraries. I don't know when Google Play added support for ABI specific APKs, maybe that was a factor too (if you have to have everything you support in the APK, then you'll be careful about what you support)

[1] https://www.pcworld.com/article/414673/intel-is-on-the-verge...

[2] https://www.cnn.com/2019/05/22/tech/qualcomm-antitrust/index...

[3] https://www.reuters.com/article/us-qualcomm-antitrust-idUSKC...

No, For x86, They were fine when all mobile CPU's where Single and Dual core. Intel actually had upper hand for a short time thanks to hyperthreading. But once Qualcomm and other ARM SOCs jumped to Quad core, Intel CPU's where power in-efficient and slow compared to other ARM SOCs. So they gave up Smartphone and concentrated on tablet chips for Android and Win8 devices. Later they gave up the Android tablets mainly due to cheap ARM chips from Mediatek and others. As for MIPS they gave up on making SOCs for Android after Imagination Technologies acquired it in 2013. Also keep in mind Smartphone's where growing double digit market share in early 2010's and developers were definitely eager to support whatever new architecture to get market share. Even though there is no x86 smartphone or tablet anymore, the app support is quite good thanks to Chromebooks, Google Play Games for Windows and Android app support in Windows.

Intel had / would have had few significant issues at the time competing on the CPU side of thing. What killed them in phones was the radios. They sucked at them, and buying a discreet chip for it hurt margins and efficiency too much.

There are quite a few x86 Chromebooks, millions. If you have one it is kinda surprising just how many Android apps run on them. (Or is it all emulated?)

The not-jvm apps should just work. Apps using binary libraries may be AOT-translated by Google or be jitted on device. The tech was there about a decade ago specifically for Android (look up Houdini) but in general is as old as the hills.