Talk is still ongoing, but Chelsea is still reluctant to pay what MU wanted. They're a club with smart business, and they have some left wing at this moment. They will patiently wait until MU will agree to let Garnacho leave with their demanded price.
Your statement gave vibe like Chelsea were rushing to get Garnacho, while the fact, they're not.
It seems like this Chelsea of a team are strategic in their business. They want to pay less for Garnacho but wanted to still give Manchester United less money in signing of Sancho and at some point the deal broke down. Although, it was an option to buy after the loan spell, though it's still within the rules to either buy or not.
Based on age and skill I think I'll prefer Garnacho over Sancho, he's a player with lots of talent and could be a star player for Chelsea in future if they sign him the only thing I'm worried about is Garnacho's attitude, if he could be disloyal to a team he graduated from their youth academy then there's a tendency that he could be a problem for Chelsea if things doesn't go his way.
It's seem the new board members of Manchester United have learnt from the mistakes of the previous administration, that's why they're not giving in to Chelsea's tactics else Garnacho would've been Chelsea player by now, Chelsea needs him to replace Madueke.