I find for games like GTA it's really not that hard to play with a controller in your lap, and just rotate when you get in/out of a vehicle.

Controller triggers work because of the drivers on PC. Keyboards and mice do not offer this same type of input, it's just pedal to the metal or not at all. You've got to just find the speed you want and dance with the pedal (button).

Some games use the scroll wheel to toggle between different movement speeds, although the option is pretty rare.

But you can also just use a controller on PC

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There are analogue keyboards Erich allows you to vary the input amount depending on how far down you press the key. It's a lot harder to control than a joystick.

Really, most games don't require analogue input. The biggest exception is driving games which is where a controller or wheel is preferred over a kb/m. In GTA speed runs for example, runners will switch from KB/M to controller on the fly.

There are mice and keyboards with analogue inputs (optical switches usually programmed to emulate a controller trigger input)

The issue is having GAMES recognize that AND regular keys at the same time.

We're only recently getting games that allow BOTH inputs ("controller" and keyboard) to be accepted at the same time.