They don't have any saving??
Nah, he's really bad at investing. The first thing you learn in to only invest money that you're willing to lose.
On the other hand he doesn't seem broke broke either, and the DIY* parts of the wedding still doesn't make it free, it just knocks off a zero from the final cost.
So it was probably more like "we can't spend $300 000 on a wedding anymore because we only have half that at best and that money is needed as the seed egg towards being able to afford getting kid(s)".
(He's still a bit bad because he hadn't made the wedding money "safe" already, but he takes after his dad I guess.)
*(About the DIY bit I reckon it's fine he was confused about it despite having used it in the past - it was probably at least 5-8 years ago since they last did anything major in the DIY way - and even if not he might just be confused about the concept that even a wedding of all things could be DIY)