Months, sometimes years go by because the firing process is so uncomfortable and awkward. This reluctance to face the situation does damage to not only the company’s finances (for larger companies it could cost millions) – but damage to team members who must suffer and/or compensate for the unfortunate hire.
Bottom line – it is far more humane to let someone go when the truth becomes obvious, rather than put them through months or years of bad or mediocre performance reviews they can never hope to correct because they are simply not the right fit. Ideally, by releasing them, they can find a position that is better suited to their talents. Additionally, by offering truthful assessments and suggestions – it could bring clarity for the next job search – hopefully for everyone involved.