Yesterday, the UK still had over 18,000 Coronavirus cases, and around 700 deaths. Numbers of cases are slowly coming down, but very slowly. It's hardly surprising that we can't ease up too much into the Tier system.
The Government putting York into Tier 2 will hit many businesses hard as it is tougher than the restrictions in Tier 2 before Lockdown. Even more important that Govt supports those businesses forced to keep closed & supply chain.