Recently updates to the NEC (National Electric Code) have required solar panels and other solar power products to change up connectors to MC4, also known as locking connectors. MC4 connectors have been more common in Europe before they became required in the USA. The revisions to the NEC in 2008 require solar power product manufacturers to update their offering with lockable connectors for compliance purposes.
Older MC3 connectors could potentially pose a safety hazard since they can accidentally become undone. The industry has moved towards the MC4 as a standard due to NEC’s influence it has over products that are offered in the solar power marketplace.