Right. Server replacement is ~5 years but it's staggered. So you'll gradually roll out new servers & gradually decommission old ones (with a rapid decommissioning phase towards the end of the server lifetime). However, not every company will adopt AMD processors when they first become available OR they may hedge their bets & do a mixed blend (e.g. Amazon offers Intel & AMD for their customers). Both of these are why it'll probably take 5 years to start seeing the initial impact & longer to see the full impact (e.g. AMD start exceeding Intel marketshare) for the early majority/later majority & laggards to adopt.
As far as being unable to buy AMD based servers I don't know. There's certainly a lot of announcements about it:
https://blog.cloudflare.com/technical-details-of-why-cloudfl...
https://www.crn.com/news/cloud/new-google-cloud-vms-with-amd...
https://aws.amazon.com/ec2/amd/
https://azure.microsoft.com/en-us/blog/announcing-new-amd-ep...
Obviously it's hard to know how many they've rolled out but I think it's more than a trivial amount. I'm suspicious of the graph because I don't know how they're capturing that data.