The UK literally handed HK to China without giving the people of HK much say in the matter.
They should’ve protested back then, but didn’t. And it wasn’t simply a matter of sheep to the slaughter. There was a lot of ethnic pride involved and a sense that they were glad to be rid of the British.
Unfortunately, Great Britain found it necessary to honor the lease and its term for expiration. It may be argued that the termination of the lease could have reverted control back to the Chinese government in Taiwan, but the various legal impediments to doing so are also reinforced with the practical problem in which Hong Kong was militarily indefensible against an invasion by the Peoples Republic of China (PRC).