The first time I heard about bond curve offering was when I participated in DIA bounty, that's what the project team decide to use to raise funds and I was surprised it went so well, not many projects are using this strategy but the truth is fundraising ways aren't that different from one another and what matters is how good the project plan to be nd how pro are the team
Most likely because the level of difficulty is way higher for a BCO than just coding an ERC20.
A BCO is like a Decentralized Exchange, basically.
