Floodwater isn't water. It's opaque raw sewage with hidden bits of wood and often metal moving around in it If the water's moving fast then a regular tree branch is a baseball bat to your shin and a piece of roofing tin is a hidden guillotine A zit or shaving cut is a door for necrotising bacteria

Also snakes!

Hell the diseases alone make even standing floodwater dangerous. Like "Not only will this kill you, and not only will it hurt the entire time you're dying, but it'll take fucking forever, too"

Your car will float just enough so the tyres lose traction on the muddy road, then once the engine drags it face down into the deep the water will pour in through the air vents and firewall wiring ports. Once the power's out you can't wind the windows down. Water is HEAVY and you can't open doors.