I wonder if the reason it's perceived as "easy" is because companies are flying under the radar. In my experience, you get a bit of leeway until the country you're selling into starts to notice and demands you start collecting and paying sales tax. Perhaps the fact the US is split across jurisdictions internally means tax authorities don't have a very clear picture until the company gets big enough.

Either that, or more companies are using third parties who mask the complexity for them. Kinda like a duck looking serene on the water but its feet are paddling furiously to keep moving.

When you're inside a jurisdiction, you don't really have the option to ignore the law for long because the tax authorities will come knocking sooner rather than later.