Most employers will not hire workers who haven't had a job in two years, so how fair is this?

Most employers are allowed to set their own criteria. Someone who is currently employed is perceived to have up-to-date skills, and thus need less of a learning curve.

And you know this based on.....What????

Not true.. I was unemployed for two years and easily got a job the week I decided to start looking, I was gainfully employed the next. You need only keep up your skillset in the interim. In fact, unemployed individuals are much more attractive to hire due to their immediate availability and eagerness to work, as opposed to employed individuals tendency to languish in developing their skill sets outside the scope of their currently assigned duties.

As a rule those with jobs are much more attractive to potential employers. There are exceptions, and certain skills that are always in demand i.e. nursing. And it makes a difference why a person has not worked in two years. Were they home with a new baby?  Or were they watching soaps?