Why did adoption slow down after a sudden rise? I guess some countries switched to ipv6 and since then, progress has been slow? It's hard to infer from the graph but my guess would be india? They have a very nice adoption rate.
Sadly here in Canada I don't think any ISP even supports IPv6 in any shape or form except for mobile. Videotron has been talking about it for a decade (and they have a completely outdated infrastructure now, only DOCSIS and a very bad implementation of it too), and Bell has fiber but does not provide any info on that either.