Today, we at SFC, along with our OpenWrt member project, announce the production release of the OpenWrt One. This is the first wireless Internet router designed and built with your software freedom and right to repair in mind. The OpenWrt One will never be locked down and is forever unbrickable. This device services your needs as its owner and user. Everyone deserves control of their computing. The OpenWrt One takes a great first step toward bringing software rights to your home: you can control your own network with the software of your choice, and ensure your right to change, modify, and repair it as you like.
The Linksys WRT54G did not run OpenWrt by default and the original OS does not even remotely resemble OpenWrt. What OpenWrt did use from the original OS was the Broadcom wireless driver because it was closed source (and a similar kernel version, so the driver could be used), since there was no driver in the mainline kernel.
But to try to answer the question, this device has been designed by the OpenWrt developers to fit their needs (and their users needs). Other routers running some variant of OpenWrt on them by default were designed by companies unrelated to the project. They most likely used OpenWrt because it was convenient to them. Their intentions weren’t usually the same as the OpenWrt team’s (repairability, easy to unbrick, etc.). Not that there is anything wrong with that. I like GL.Inet routers.