Personally, I think it's because of the typical asian Chinese mentality that prioritizes ego or face-saving, need to let the whole world know or people would get the wrong idea that the marriage was a quiet one because of other reasons. This is why I avoid weddings at all costs.

But some truly does it big simply because they want to share the joy, but I personally prefer a small, quiet wedding if possible. It's nice sharing your moments with people whom you really love and know over a huge group of people that you barely know. Later dad invites his friends, mom invites her friends, brother invites his friends, sister invites her friends, then you and your spouse's friends. Then later the cousins, and it just extends and cousins might end up bringing their own friends to the dining table