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Is it the fact that HBD is limited to 10% of HIVE?

Yes, this is the big one. Currently the proposal is to increase it to 30% with the next hard fork, but that's still a very conservative value.

Could you point me to an article if possible?

This is a good starting point, and I've added some comments to attempt to clarify the key protection:
https://hive.blog/hive-167922/@taskmaster4450/hbd-defenses-how-hbd-is-different-from-ust