It's part of a global health strategy to eliminate viral hepatitis as a public health threat. One paper on that, on the introduction of it in the UK : https://pmc.ncbi.nlm.nih.gov/articles/PMC6422463/
In May 2016, 194 member states of the World Health Assembly – including the UK – signed up to the first ever Global Health Sector Strategy (GHSS) on Viral Hepatitis to eliminate viral hepatitis as a public health threat by 2030. This strategy set global targets for viral hepatitis, with a goal of a 90% reduction in incident hepatitis B (and C) chronic cases and 65% reduction in mortality by 2030. In pursuit of this ultimate elimination goal and recognising that hepatitis control through immunisation is an essential foundation of a hepatitis B prevention programme, the World Health Organization set out vaccine coverage targets for both universal childhood immunisation and selective immunisation to prevent mother to child transmission.
As the section on epidemiology makes clear, it's a nasty infection, and children and infants are more likely to progress to chronic disease if infected. So universal immunisation, which is thought to provide persistent immunity for 30 years plus, has a clear justification to provide both individual protection and reduce the risk overall.