The manufacturer usually modifies OpenWRT/QSDK to support their device. AFAIK, most of the time individual components from the device (CPU, Ethernet switch, wireless chip) are already supported in OpenWRT, it's just that the specific combo that the device contains just isn't there yet. This configuration is done with the device tree. On top of that, some manufacturers (Tp-Link, for example) don't use the standard OpenWRT sysupgrade image format, so the device rejects the new firmware that you try to flash.
You're correct with iOS, but Android allows browsers to have their own rendering engine (see: Firefox with Gecko.) Microsoft just didn't want to invest in porting EdgeHTML to Android.
This article is a little sensationalist. If you don't want to trigger the Assistant, you can turn off the "OK, Google" keyword. If you don't want your voice data to be used for research/analysis, there's a checkbox for that too.