Because when we purchase the system it is with the latest drivers and utilities that what my OS need.
Some drivers can already be old at the time of purchase. The system might have been waiting in the store for a few months. (Although admittely drivers rarely evolve that fast.)
So why they become old after some time.
The same way normal programs become old: if version N has some bugs, developers will release version N+1 with some bugs fixed and/or new features added.
What is the best way to know that my drivers are being old and cause the system slower?
In software, "old" does not automatically mean "slow". Very often, old drivers work just fine, they simply don't have new functionality.
And if a driver has bugs, they will be noticeable immediately when using the device – not when it becomes "old".
How can I keep update them time to time automatically if it is possible?
Some manufacturers publish drivers for their products on Windows Update. They would appear under "Hardware (Optional)" whenever a new version is available.
Others provide an update check on their own websites – for example, Intel has a "Driver Update Utility" that scans your computer.
There are programs that scan all installed drivers regardless of manufacturer. Unfortunately, I cannot recommend any; and you should be very careful with programs found in Google.