From the numbers I'd say that it's US that has unexpectedly low number of Bitcoin nodes, not that Germany would have too many.
I wonder how people will explain both Salvador and Nigeria having ZERO nodes
The logic is simple, assuming that both countries have shite internet connections - and this is to say nothing about connection downtimes - downloading a third of a TB in these countries, on your private home connection (because let's face it, do you really think you'll be allowed to host a node on academic faculty hardware?) will take simply too long, and the amount of GB that's passed around in the form of block messages that will follow makes the IDB unfeasible even if you stretch it across several weeks, you're node will always be dozens of blocks behind the tip.
There is no such a thing as "too many" nodes in a country, there is however a lack of nodes in too many places.
...there is such a thing as too many nodes in a particular ASN. e.g. an entire data center burns down or otherwise has an outage, and dozens of nodes go down with it.