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Although it sounds very strange to you, there are some people who live in my country and it costs them something to get the money, and 100 or even 500 usd if you can raise them a lot, at least so that they can buy their food supplies and basic things. Of course, not all of them are in the same conditions, but the vast majority are, due to the high inflation, to tell you that some people in their base salary is less than 10 USD, especially those who are professionals, the teachers are demanding that they raise their salaries. and apparently the government will not raise anything, in third world countries the problems can be very precarious, sometimes the countries in Europe and the USA are very privileged.
I'm not denying that there is poverty in the world, but you said, quote: "...
few people in the world have that ability to spare money...". The "few" is a massive exaggeration. The vast majority of people would spend at least some portion of their money on the things they don't need or things that are not good for them (sweets, junk food, alcohol, tobacco etc), which proves that they indeed have some money to spare.
And even in a dirt-poor country, losing say $5 will not make any significant difference to your life.