"the people have voted and the people wants to leave the EU"
The judges' ruling supports the sovereignty of parliamentary democracy.
Let's take an analogy, albeit an imperfect one. During a general election, people might vote overwhelmingly for a Conservative government that has campaigned (say) to reintroduce grammar schools. But when the government decides to carry through that policy, they can't just unilaterally reintroduce grammar schools. They have to put the exact detail of the reintroduction into a parliamentary bill that then has to be discussed by MPs and the House of Lords. The bill may be amended by parliament before it is finally voted on and passed into law. That is the very essence of our parliamentary democracy. People debate the arguments, they point out the flaws in the bill, they propose amendments - and all this is carried out in front of the media so that we, the voting public, can hear the arguments for ourselves.
For the government to say that it will implement Brexit without having the exact proposals scrutinised by parliament flies in the face of our constitution, our traditions and democratic accountability.