Rarely do companies and startups have the luxury to just lean back and take their time. It's a race against competitors, and everyone wants the advantage of being first.
I don't blame the devs, as much as I blame the market. People start taking shortcuts when they're judged by how fast they can crank out codes, and whether they can finish their sprints on time. You develop a culture of constantly putting out fires.
Hell, for some consulting firms this is a profitable business model: Deliver a partially working product, then spend 10-15 years on patching it up, on your clients bill.