Not a downvoter, but it’s probably because it doesn’t really matter. If you want high speed connections for multiple devices, use a separate switch. Devices that are purely routers often have only a few ports, and you can use VLANs to multiplex subnets.

External ISP connections rarely exceed 1Gb in many parts of the world (for home connections especially), so there’s not much point in a faster link speed.

And the chip itself only supports 1x 2.5Gb and 1x 1Gb, so the choice was made for them. Maybe they could have limited both ports to 1Gb to avoid a perception that one port is hobbled.