I wouldnt pay too much attention to the number of servers - 90% of them have only one user or very few users and host no communities of consequence. Most active communities are hosted on about 3 or 4 instances.
In about 6 months all the admins of those tiny instances will be considering paying the bill for the next year of domain / hosting and many are likely to pull the plug.
This process doesn't reflect a weakness of Lemmy IMO, it's just because of a certain amount of centralisation that has happened.