Not allowing kids to believe in Santa

Stupid topic, and I don't know why, but it makes me sad that my SOs niece and nephew are told that Santa isn't real. They are 3 and 5 and ive known them since 10 months and 3 years. They've always been told that Santa isn't real and that everyone else buys them presents. And the little ones tell other kids who do believe in Santa that hes not real. I feel like believing in Santa is a right of passage for kids and its part of the fun for them during the holidays. Maybe its just the way I grew up. But is it odd to make it known that Santa is not real before a certain age?