Note that prior to its license change ScyllaDB was using AGPL. This is a fully FLOSS license but may have been viewed nonetheless as somewhat unfriendly by potential outside contributors. The ScyllaDB license change was really more about not wanting to expend development effort on maintaining multiple versions of the code (AGPL licensed and fully proprietary), so they went for sort of a split-the-difference approach where the fully proprietary version was in turn made source-available.
(Notably, they're not arguing that open source reusers have been "unfair" to them and freeloaded on their effort, which was the key justification many others gave for relicensing their code under non-FLOSS terms.)
In case anyone here is looking for a fully-FLOSS contender that they may want to perhaps contribute to, there's the interesting project YugabyteDB https://github.com/yugabyte/yugabyte-db
I think AGPL/Proprietary license split and eventual move to proprietary is just a slightly less overt way of the same "freeloader" argument. The intention of the original license was to make the software unpalatable to enterprises unless you buy the proprietary license, and one "benefit" of the move (at least for the bean counters) is that it stops even AGPL-friendly enterprises from being able to use the software freely.
(Personally, I have no issues with the AGPL and Stallman originally suggested this model to Qt IIRC, so I don't really mind the original split, but that is the modern intent of the strategy.)
I think the intention of the original license was to make the software unpalatable to SaaS vendors who want to keep their changes proprietary, not unpalatable to enterprises in general.
Rightly or wrongly, large companies are very averse to using AGPL software even if it would cause them very little additional burden to comply with the AGPL. Lots of projects use this cynically to help sell proprietary licenses (the proof of this is self-evident -- many such projects have CLAs and were happy to switch to a proprietary license that is even less favourable to enterprises than the AGPL as soon as it was available).
Again, I'm happy to use AGPL software, I just disagree that the intent here is that different to any of the other projects that switched to the proprietary BSL.
I haven't actually talked with Henry Poole about the subject, but I'm pretty sure that was not his intent when he wrote it.