Most professional magazines are more motivated by physical and online 'sales' rather than Impact Factor. For instance, I have just published in 'Nursing Standard' last month after they invited me to publish a CPD article. Their peer-review processes are rigorous and they produce quality outputs. It has a long established history and reputation - and this will maintain them beyond impact factor alone.
Impact factor is determined by averaging the number of citations a journal receives and the average number of times that articles within the journal are referred to by other articles. Simply put, the more often a journal's articles are cited, the higher its impact factor.
To gain an impact factor (IF), a journal must be indexed and must have been indexed for three years. Since IF is computed based on citation data and number of manuscripts, the reasoning for theee years wait is to allow accumulating such data.