Eli5: Why did we invent wheels for cars instead of legs? Wouldn’t cars with legs be able to manoeuvre around uneven lands easier?
Legs are pretty complicated, wheels are really simple. Wheels also are better at carrying a load with less energy (this is why you can go faster on a bicycle than you can run)
It takes more energy to move legs than it does to move wheels. It takes some energy to spin the axel which spins the wheel but, even after cutting off the source of energy the wheel will continue to spin as it’s gradually slowed by friction. Legs however, require a constant source and once it’s stopped they will fail to move. You can test this yourself by running and then freezing your legs and you will likely find that you fall immediately to the ground. Then you can take a bike and lock the handle bars in place before giving it a push and you’ll notice that it travels a ways before it slows and tips over.
Wheels didn’t need a lot of invention. (Cut a rounding trunk into cross sections). They don’t even need to be perfectly circular to assist with moving things.
Legs, on the other hand, are fairly complex mechanisms. They need hinges, linear actuators (muscles) and something that balances and coordinates their movement. This is hard to make work purely mechanically – it is only with computing and advanced sensors that legs are even feasible that can adapt to terrain. Simple mechanical legs might work on flat and even surfaces but that is exactly where a wheel works even better.
Legs are also hard to make fail safe – a single failure very likely leads to collapse whereas a wheel not working might, at the very worst, just stop moving.
The wheel is an incredibly simple yet very effective shape when it comes to moving across land. The mechanisms by which vehicles use wheels are *also* fairly simple.
Making a vehicle that used legs is very doable, but it would not be able to move at the same speeds as any wheeled vehicle. One issue that would definitely pop up would be damage to roadways; concrete etc isn’t really impact proof past a certain point and if every vehicle had legs, the roads would be in shambles