These very expensive parties seemed insane to me, but now I get it.

Imagine this fantasy scenario where you are stupid and mangina enough to get married.

Before the wedding, you get cold feet, you're thinking - this is retarded, why am I going through with this, I need to put a stop to it. But you don't.

Less than two weeks into the marriage, you're thinking "Why is this god awful shrew yelling at me all the time, is this how the rest of my life will look like? I'd better bail before I gotta pay alimony".

But you don't.

Why? There was a wedding. It cost a lot of money. Your parents probably paid for a portion of it, or you even went into debt. Your relatives and friends came to the wedding. They brought presents. All this social pressure - all because of the wedding.

There would be social pressure even without a wedding, but this expensive, vapid, irrationally lavish party is the nail that actually keeps you in the coffin.