The difference is simple. If you have 20 million, 20 dollars is 1/1,000,000 of your net worth.
If you have 200,000, it is 1/10,000
If you have 20,000, it is 1/1000 of all you own.
The less you have, the more precious every dime becomes.
It is why Christ saw the widow's mite as a great contribution--it represented a substantial portion of all she had.