The WebThings Gateway does support OpenWrt if the router is beefy enough (decent app processor, RAM, and flash). Most cheap routers wouldn't work. If you are a savvy OpenWrt user see: https://github.com/openwrt/packages/tree/master/lang/node-mo...

The Turris OS that runs on Omnia is a customized OpenWrt build that lets a user plug a USB memory stick (with the Mozilla WebThings Gateway image, and only that image on it) into the Omnia, hold down the reset button until the 4th front panel LED lights, let go, and wait until it installs and the "WebThings Gateway XXYY" SSID appears. Then connect to it and proceed with the setup process. Suggest other hardware to potentially support on Mozilla's Discourse "iot" channel. Or the mozilla-iot/gateway repo on github.

Probably the flexibility of that router having 3 MiniPCIe slots for the wireless card(s), from the standpoint of ease in firmware development. The cheaper routers with embedded radio chipsets range from very good to crappy support for open source firmware. But, few people are going to be interested in a 350$US product, when equivalent is available for a fraction of that.

This was my question as well. Why fork? Why reinvent those parts of the wheel? Good luck reaching device compatibility parity...

TurrisOS is based on OpenWRT with some additional stuff like auto-updates.