Because what we're trying to measure is actual supply and demand of labor, and how hard it is to get a job. Someone saying they want a job but not doing anything doesn't tell us anything.
Someone who actively looks for a job....Contact employer directly/interview, Contacted public employment agency, Contacted private employment agency, Contacted friends or relatives, Contacted school/university employment center, Sent out resumes/filled out applications, Checked union/professional registers, Placed or answered ads, or other, such as had an audition or bid on a contract..........did something that could have gotten them a job and did not.
If someone did nothing that could have gotten them a job, then they could not have gotten a job, no matter how much they say they want one. As far as getting a job goes, someone who says he wants a job but is not trying to work is no more likely to get a job than anyone else not trying to work.
Those not looking who say they want a job are counted...
A-38. Persons not in the labor force by desire and availability for work, age, and sex
But look...of the 6 million people not looking for work who say they want a job, 3.2 million have done nothing at all about getting a job in the last year (this includes teenagers who've never had a job and never looked for one). Do you think they're really a good indicator of how easy or difficult it is to actually get a job? Do you even think it likely they'll start to look soon?
And further...of those who did look in the last year but not the last month, 593,000 could not have accepted a job if offered on a plate. What do they tell us about the job market?
That's what it boils down to...the job market. People not participating in it can't tell us anything about its condition.