There are cars with inboard brakes, although not recently. From a packaging point of view putting them out at the wheel makes sense, since there's a lot of space you're not using otherwise.

It's hard to fit inboard brakes to front wheel drive cars because there's so little space but Citroën managed it with the 2CV and various derivatives, and the GS/GSA/Birotor family. They had an inline engine with a very compact gearbox behind, with the brake discs (drums, on very early 2CVs) right on the side of the gearbox.

You got lower unsprung weight and possibly more usefully the kingpin was aligned with the centre of the tyre, so when you steered the tyre turned "on the spot" rather than rotating through a curve.

Some old Jags and Alfas had inboard discs on the rear axle, which was of course rear wheel drive. They were a bit of a pain to get at.

I’ve generally assumed that brakes are in the wheel because they’re not all that massive, they get decent cooling airflow in the wheel, and they can produce enormous amounts of torque.