Why 2 keyless remotes in my car?

Both keys are recognised as separate entities by the car. So because it knows which key is in use, the remote locking computer knows which rolling codes it should expect for each key.

Sometimes they do go out of sync, but when that happens the vehicle owners handbook will state how to re-synchronise the keys.

I wonder if your job involves logic or thinking?

Why don't you give your defective idea to the car dealership and find out their response.

If I was a car manufacturer, I would provide 2 remotes for each car in case there might be 2 main drivers for the car.

Damn, yea, weird. I got two remotes that work with my car too. I am confused too. Rolling codes? Har dee har har.

In case you lose the main, you have a second to use. It will work for a time but eventually will not, and possibly the battery will die before you try and use the second remote. At that time, you go to Youtube and watch a video on how to program the remote(s) when you actually need to use them.

One is a spare?

The car should "know" which remote is being used, and can keep track of the code sequence, which isn't truly random but calculated. If it goes out of sequence and you have to use a physical key to open the car it should re-sync as soon as you switch on.

Without knowing the exact year, make and model of your vehicle the answer can vary. On my vehicle the two remotes are designed for Driver 1 and Driver 2. This allows each driver to customize various memory settings such as seat positioning, etc.

Your car is programmed to recognise both your remotes. Understand this or not, it works. You'll be glad you have a spare if one gets lost or locked inside the car.

You get two remotes because there may be two people who regularly drive the car, or if you loose or the battery runs out on one remote. Both remotes will work, even if you don't use one for several years.