but decrease how much each person has available as resources? Essentially just throwing a lot of people into poverty?

That is not implied. Especially if we consider that the resources we waste are through supply chains rather than our own direct use. If my electrical supply comes from from a more efficient source, then my usage can be less wasteful and potentially cheaper. If my city continues to improve public transport, I can actually save money and use less resources in daily transit. Products we consume have serious potential to conserve resources at a mass scale, and often it even saves them money due to paying less for resources needed in production. A lot of waste also comes from overproduction, think of those Dunkin' Donuts end-of-day-disposal videos. We make far more than we need in so many areas.

Furthermore, the most wasteful people are a minority of the mega-rich. You and I probably don't need to cut down much on jet fuel costs. People close to poverty usually aren't (directly) wasteful, hell, some of them actually reduce waste through dumpster-diving and recycling schemes.