It’s simple.
The poor (in fact it’s not the poor - it’s the middle class and even the lower side of the upper class) spend their TIME for remuneration, i.e. for money. Their main method to generate money is to INVEST TIME as an employee.

Now, the time is valuable. I would say you don’t just invest time - you also invest your talent, your beautiful years, and even your freedom. What for? For money - which is a source of existence. Where and when do you, as an employee spend your hard earned money? Well, outside the working hours - if there is left some free hours.
This is sad, because employees don’t have a growing opportunity. When you invest your time - your hour can cost $20, then $30, then $100, and there is always a limit - let’s say $500 for the highest paid positions.
For those who buy your time it’s a great deal - they exploit your time and your talent, which is why you should negotiate your time very precisely.

When you invest money - you can enjoy your free time and can multiply money without having a boss, having to wake up at a precise hour or put many limits to your life. When you invest money - you have a huge growing opportunity.
Look at the wealth evolution of Buffett:

He has $75 billion today. Do you see the dynamic of growth? It’s because he invested money and not just his time.
I hope this helps!