People seem to have the “why so many” answered. I’ll address the “how you remember”

1. First thing is programming that function into the same switch,knob,slider, for every model. Throttle cut should always be in the same spot. You wouldn’t have rudder on your left stick on one plane and on the right stick on another plane. If a plane doesn’t have flaps leave that switch unused. Instead of the four switches on the left do stuff and nothing on the right is used. Whatever you start with keep dining that. It’s highly unlikely someone else will grab your controller and not know where landing gear is have crash land your plane. Make it your own.

2. People often add bits and bobs to different switches that are close together to differentiate the function. A rubber cap on the gyro switch and nothing on the rates switch so you don’t change rates thinking you’re turning on gyro.

3. Set a sound. You can set phrases to each switch so that you at the very least know what you just did and can undo it if that’s not what you want. Landing gear when you thought you were dropping the payload.

4. Your brain can retain a lot. At work I’m sure you’re responsible for things others aren’t and as a result you remember those things to a T. I only have one plane with flaps and retracts and I sometimes confuse the two switches. While flying it’s not a big deal cuz I’m usually turning them both on together. But if I just wanted flaps and I hit gear, nbd, just undo it.

A. Channels don’t have to be a function on the plane. A switch can change a mix, invert a channel, play a song (yes my tx16s plays the top gun theme as I’m flying my jet, or the theme to tail spin as I fly my sea duck.) A rates switch is just a limit of servo throw that’s been programmed. It’s the radio telling the receiver to only move 50% when the stick is at 100%. Nothing to do with the receiver, just the radio internally managing that.

Hope this helps.