I guess it’s because the LED widget does some PWM simulation in the background, so it requires a value of 255 to turn it on whereas a regular physical LED simply requires a HIGH or LOW (1 or 0) to turn it on/off - depending on how you’ve wired the physical LED.
I assume that you’re using an Uno?
There are techniques for reducing memory usage when coding, such as taking care which variable types you use, which libraries you include, and use of the ‘F’ macro when doing serial prints.
However, you’re probably better-off using more appropriate hardware for your project…
Pete.