Why don't BRK and Drakelowe connect?

Kwoung

Just curios as Ash and Brindle do, as does Ales and Dragonclaw.

edges_endgame

It does for EP and AD

ExistingRug61

Actually Drakelowe and BRK only connect directly for EP (although I guess technically they can be connected for AD but this is via Alessia).

Connections to the outer three keeps (Brindle, Drakelowe, Dragonclaw) vary depending on your alliance - you only get connections from an outer keep to home emp ring keeps. This is indicated by the little coloured "lock" symbols on the transit map - any link with the coloured lock symbol only works for the alliance indicated by the colour of the lock.
So
DC: Ash-Brindle and Aleswell-Dragonclaw
EP: Chalman-Dragonclaw and Blue Road Keep-Drakelowe
AD: Alessia-Drakelowe and Roebeck-Brindle

Similarly, links between the back two keeps and the centre keep only work for the home alliance, also indicated by the coloured lock symbol on those links.