In many places, even in the US, houses are built on stilts. It’s not so new or novel. You can see those houses in the Florida Keys and Louisiana bayous without looking too hard.
But away from actual riverine living, people who normally live “on land” next to rivers also need daily transportation. And you can’t drive your car to a stilted garage. If you could, you still couldn’t drive out of the stilted garage into a deeply flooded roadway. So you’d still be stuck, stranded, cut off. That won’t work (people’s livelihoods being what they are in our economy) for the long stretches of time that floods can last, so it’s an option that people don’t want to pursue. Not practical, given the world we decided that we wanted – and set out to build.
Plus, as others have already described, the Army Corps of Engineers has had a two-fold mission: to improve river navigation by more and larger shippers, which means dredging deeper and wider – and straighter – channels, and maintaining optimum flow year-round, plus preventing floods of the riverbank communities with higher levees. Those missions are essentially at odds with each other.
Every time rivers are dredged and made straighter, to aid navigation, that speeds flood waters downstream. So flood stages that used to take longer to develop, giving downstreamers a better chance to get away (and more time – and places – for waters to dissipate into oxbows and sloughs), it makes the downstream effects faster and the water higher when it gets there.