You decide not to feed it because it’s not your dog - it’s not your problem. But your whole house is completely stocked with food. You throw out large amounts of table scraps and leftovers daily.

How many people would consider that to be evil?

Internally the person can justify his actions "You feed a stray dog one time, it will nag you forever, maybe call up his buddies because there is free food, and now suddenly you have a pack of stray dogs on your farm that are causing all sorts of trouble". Such nuances are always present(I will stop with the dog analogy, because your original example and my addendum, dehumanizes people in need to dogs). but such is the harsh reality, that often arises with a direct personal transfer of wealth, people tend to form a dependency on the table scraps and those that provide them(even though they are losing literally nothing) resent it.

The solution you may ask to greedy billionaires and hungry homeless people, SOCIETAL or GOVERNMENTAL INTERVENTION, think about it, its the failure of whoever the fuck is in charge that a select few of their citizens have exploited the system so well that their wastage is equivalent to the GDP of a small country, and similarly there are many people that only dream of a roof over their heads!!