[486sx33]

Some routers specifically allow openWRT.. example, Routers like the GL.iNet GL-MT6000 (Flint 2) and TP-Link Archer AX6000 come with OpenWrt pre-installed and are designed for easy OpenWrt use.

[Benanov]

...usually because they have a fork of the codebase, and it's not vanilla base OpenWRT.