Why is this not concerning? Two reasons. Firstly, the only numbers we are tracking here are public nodes. These public nodes are generally used to route your payment through to reach its final destination. We don't know how many private nodes there are, which include the most commonly used Lightning wallets such as Eclair. It is likely there are far more private nodes than there are public ones. Secondly, capacity is not the same as volume. Capacity is needed to route a transaction, but says nothing about the number of transactions or volume of BTC being moved through LN
Why do I have a feeling that some bias is at work here?
So you basically assume that since we don't know the real number of Lightning Network nodes, this number must be huge. To me, this is a loose assumption. Further, even if you agree that capacity is not the same as volume (the point which I agree with too), it does in fact say nothing about the number of transactions or the amount of bitcoins being moved using this capacity. The meaning being that there can as easily be none (or next to none). Assuming otherwise, and otherwise being a multiple of that capacity, seems even more far fetched to me
The bottom line is that we don't know the real situation other than what we see at 1ml.com. But what we know for certain is that Lightning Network is not widely used where it is expected to be used, i.e. in places like cafés, pubs, bars, maybe even brothels, and similar institutions. This is what counts in the end as Lightning Network is supposed to fix the innate problems which prevent Bitcoin from being used as a means of payment (read, private nodes are completely inconsequential). But if it is still not used for that, how can Lightning Network actually help here?