I think that's a misunderstanding. They don't lay charges against dead people. The only reason to lay charges is to justify arresting them and keeping them in jail, pending a trial.
The charges against them in Dr. Dyck's death were withdrawn.
"When RCMP confirm that the bodies are those of McLeod and Schmegelsky, the charges against them in Dyck’s murder will be discontinued, British Columbia Prosecution Service spokesperson Dan McLaughlin said. “This will end the prosecution and the involvement of the BCPS,” he told local media."
Canada manhunt: police are 'confident' two bodies found are fugitives
Police have focussed on writing this complete report in order to wrap up the case and put it to bed. They definitely fast-tracked it because of public interest. I wonder whether the CBC stories about questions sent to the Prime Minister's Office encouraged them to just publish what they had and not wait on any more lingering details, like date of death.
If they had been arrested, they would have faced charges eventually in the deaths of Lucas and Chynna, but it wouldn't have been a rush to do that, either. It takes years for murders to come to trial in BC. Police focus their initial efforts on collecting exhaustive forensic evidence while the crime scene is fresh, and getting the suspects arrested. Then the case usually goes into the back of the queue while detectives prioritize other, urgent crimes.