Flash is to web dev as Excel is to desktop applications: it "sucks" but is also arguably the single best tool the entire field has produced. The technologies that might replace Flash are "better" but also so much worse that they aren't even close to actually replacing it, years on—and, yeah, that's mostly about the authoring tools, which were not just excellent, but also de facto free for hobbyists (thanks, piracy) when Flash was in its prime.