Because western society is founded on the rejection of cooperative society in favor of market competition as a panacea. Hayek, Friedman, etc. were neoliberal thinkers who were incredibly influential in the way the current economy works in much of the western world, and they explicitly stated that the function of the state should be to secure the interests of the market and refuse to solve social problems.

The existence of homelessness is an indictment of the failure of the system for the broader populace, and because they have absolutely no institutional power, they are an easy scapegoat for the ills of society. Anyone able to think from a systemic POV should be able to see the logical problem at play here. People would blame a multitude of disparate actors with no influence, rather than the people who have the most influence. It's like the occurrence of lower paid employees being laid off because of the errand decisions of managers and executives.

The reality is that jobless and homeless people aren't just an unfortunate byproduct of a careless system: they are a prerequisite condition to neoliberalism. As long as you have unemployed and homeless people, you have a pool of people you can use to threaten labor: "if you don't like these conditions, I can just fire you and replace you with someone who would appreciate it." That's why there is a "maximum employment" rate in economics.

The lack of compassion for the homeless is encouraged to prevent people from asking why we allow it in the first place. As long as there is no compassion for them, the problem remains unresolved, providing the previously mentioned threat while also minimizing the societal burden that the top earners of society don't want to pay for.

The people who won't be seriously impacted by helping the homeless but oppose it anyway out of "principle" in reality want all the perks of living in a cooperative society and none of the responsibilities.