SkillsFuture or how the government gives you money without giving you money.
Whether due to family, company, mental well-being, never wanting to go back to school and face the eternity of memorizing info and regurgitating it during exams, etc, not everybody have the time or inclination to take courses.
If you're old, you're old and no amount of new and innovative courses can help you. Unless you're old but have unique skills and experiences such as a helicopter engineer or a Director in some big company and by then you don't need to waste time on SkillsFuture courses.
I think the government is overly optimistic that employers will give you higher responsibilities and more money, or offer you a job because you take courses that is outside of primary education (uni degree) - exception being very niche and specialized fields. The problem with very niche and specialized fields is that there are more job seekers than niche and specialized fields companies - so back to square one.
While not related to why some wont take up courses, are SkillsFuture helping course companies or helping the people - like the CDC vouchers were originally intended to help hawkers by restricting usage to hawkers and coffeeshop vendors.