Every so often a person would have a brilliant idea on how to solve our scaling issues. They would then disappear into a corner to invent yet-another-bird-themed-datastore. After a few weeks/months they would appear with a magical new thing that would fix all our problems and would make everybody happy. Every single time it would fail.
Having a team that is not the main team design something means that they likely didn't understand the state of the thing that they were replacing. The thing they were replacing was a bucket of edge cases non of which they knew about. The scale never looked like what they expected because in the meantime the load had changed. This was compounded by the constant desire to hire somebody external that could solve the problem for us. They would come in with ego and a feeling that they had a mandate to replace it all. Eventually they would learn just how fragile and complicated the system was, only to then be considered old guard enough to be replaced by the next wave of experts. =/
But the number one killer was that every single thing was baked into the mono repo so it wasn't like they could have just easily shimmed in something to replace the old thing. All the while that they are building in a change to the data store another dev has added 15 new features that they now have to port over. In the time it took to port those over another 20 had been added.. etc.
Just getting the okay to pause feature development was like pulling teeth and it only bought you a few weeks at best.