🇧🇪 Money that expires in Belgium: GSM gift cards

What’s the point of allowing money to expire? If you buy a top-up for a GSM account, what legit reason could there be for allowing carriers to screw over consumers on such an arbitrary basis? Indeed, if you buy phone credit in Belgium, it expires. I just bought a top-up card that had already expired because I did not notice the expiration date in tiny print.

Interesting to notice that some US states have banned gift cards that expire.