AFAIK half of those, ExaBGP and GoBGP, could be used to build a route server, but aren't out of the box, and it's far from obvious doing that would be less "wasted resources" than the investment in OpenBGPD, and at least for what's actually deployed in IXes BIRD is more or less a monoculture, so apparently the operators think the alternatives aren't so viable.
I used OpenBGPD it first around 2012.
In moment I have OpenBGPD instance with 4 x full table, so that "nothing else can handle the full BGP tables" isn't simply true. Thats not forwarding instance though, I use it as looking glass.
Handle the full BGP table while serving as a route server. OpenBGPD devs themselves admit it was inadequate at that role, mostly because adding filters was incredibly inefficient, as well as RIB updates being super slow (in a relative sense).
I have been doing full tables using Quagga in production, in multiple regions, for years.
The thing BIRD does well is being hardened against untrusted users having access (the route server use case). I'm very happy to see a second implementation that has this focus as well.
What about FRRouting, ExaBGP, GoBGP or Bio-Routing ? Yeah, wasting resources for stuff nobody needs - thanks RIPE! (what about contributing?)
Bang on, BIRD is absolutely not the only solution in this space, no idea what the author's on about