Hard Fork is required when you are changing the rules on a blockchain.

--Steem 20--+--obsolete
             \
              +--Steem 21--+--obsolete
                            \
                             +--Steem 22--+--Steemit's centralized fraud machine.
                                           \
                                            +--Hive 23--X--+-- obsolete
                                                        ^   \
                                                        |    +--Hive 24-->
                                                        |
                                                    we are here

Not all hard forks are used to create parallel universe some are just used to upgrade the technology and improve the rules. That's our case.

so for this new project not to become too decentralized, you need nodes

The other way around. But you are writing about mining, and mining is a think on a Proof-of-Work chains. Hive is a Delegated Proof of Stake. There's no mining here. On PoW chains, those who have more computing power have the best chance to produce blocks. On DPoS chains such as Hive, the best chance for block production have those with the highest approval (most stake-weighted votes) from the stakeholders.