Trump was president. The Chinese considered Joe no longer an asset and did not want to pay him and "grifter boy" Hunter anymore money. The Chinese made a major error on this. They should have kept paying.
That was like Spiro Agnew’s mistake — he thought he was still entitled to pay-offs after he left state/local politics — but bribe money is habit-forming, and it’s hard to go cold turkey, especially if, like Hunter, one has an addictive personality.