It's called liberalism because its core value is the liberty of separate individuals to do what they please as long as they don't interfere with the rights of others to do the same. The state has a monopoly on the legitimate use of violence in order that it may enforce the law. Justice, then, consists of obedience to laws against the private use of coercion, and in the fair and equal application of the laws. On this conception of the state, nothing more can be demanded of us than that we pay our taxes and stay out of trouble. In the first place, economic inequalities, as long as they result from the voluntary, uncoerced activities of individuals, cannot be understood as unjust.
Every worker is free to leave any job and seek a better one.
Employers are free to offer whatever wages they wish, and workers are free to accept or reject the offer. In fact it would be unjust to tax the wealthy in order to help the poor, since that uses the coercive power of the state to interfere with the results of the free, non-coercive actions of individuals. A second reason why economic equality cannot be made a matter of justice is that it requires giving things to people who have not earned them. This is a violation of the central moral principle of capitalist society. The state operates by laws and regulations that must be general, while the needs of individuals who are poor or sick or otherwise in trouble are particular and infinitely various.