It had been in the works for a while, but now it has formally been adopted. From the article:
The regulation provides that by 2027 portable batteries incorporated into appliances should be removable and replaceable by the end-user, leaving sufficient time for operators to adapt the design of their products to this requirement.
The intentional slowdown was directly related to battery life. They got sued over it. But if you put in a new battery, performance returns to previous levels.
Apple even tells you in your battery info settings page whether you are running with “Peak Performance Capability”.