I have experience being an author on a private curation guild on steemit e.g of something similar is @r2cornel-curate here on blurt.
I also have experience being a curator on privately owned curation guild on steemit.

Yeah they are a good but they are also covered by a sole point of failure and progress. If the investors who manages/founded those guilds decides to power down and leave after gathering a community of over hundreds and thousands of people, the entire community members could just leave because they are no longer recieving upvotes, which is hard to get from other communities which you do not belong.
This contributes to the reduction in utility value and could flaten our J-Curve in the long run as the number of users reduces. N/B the economic J-curve increases based on utility and investments. utility attracts investments
e.g of these communties on steemit which I experiecned include
@stach by @ejemai
@steemjet by @dimimp
@w-africa by @surfyogi
@agfacademy by @oracle-d
even @utopian

The utility value generated by these privately owned curation guilds droped drastically as the investors moved away.

On blurt

Things seems to be quite different to ensure the continuity and even distribution of rewards in order to retain these active users.

Yes 1 million blurt power is pretty large but some communities here on are worth it because they are large enough for a 1 million BP delegation. We also have smaller communities getting 1 million BP too and it would be neccesary to reduce the delegations of such.

I am speaking as a witness and curator of @blurtafrica @gozapata which is a very large community of people across the cotinent of africa and universities in Nigeria.

The Owner keys of these curation accounts listed above are managed by @socialgraph the blurt foundation and the curators are only entrusted with the posting keys.

we can be sure that the blurt foundation does not have any plans to power down and leave and that should assure that these curation guilds would always continue to exist and would continue to grow the utility value of blurt blockchain.

Curators have guidlines that they do have to follow and if they go against them, they stand a chance to loose their positions as curators and priviledges, when @megadrive the bursar to the blurt foundation changes the keys.

Reducing all the delegation may not be a good idea as less than 1 million BP may not be enough to manage a pretty large community of users