Why is there such a difference between US and UK judicial sentencings?

For example in the UK we have about 40 prisoners who are on a "whole life tariff "(no possiblity of parole) yet i read somewhere(not sure the date), that there were about 2700 YOUTHS, in prison in the US with no possibility of parole. So between youths and aduts you must be looking at tens of thousands. I think the UK system is way to soft.