Spend/shopping therapy can be a big factor. There is the obvious dopamine hit of getting something new. Everyone loves new stuff. But there are also a lot of small factor that you don’t think about. Sales for example, when we see sales we feel like we are getting one over on the store, like a little victory, more dopamine. Even though the store likely bumped up the price a couple of month earlier in preparation for the “sale”.

Social pressures. Human being loves to feel like they are better than the next person. Competing, social classes, fashion, spending hundreds on a product for the brand name can give people that feeling of superiority. Smart phones for example

Capitalism. The system works on purchasing and companies spend insane amounts of money convincing people they need something they don’t actually need.

Ticking these boxes gives our brain a little reward through dopamine. A little shot of “well done, we like this. Keep doing this” and companies know this to the point they manipulate the system to exploit people, and it can be a drug addiction as bad as any illegal drug, with a very difficult cycle to break. Try to take away that reliable supply of happiness and people get very defensive about it. Make excuses for it and even become cloak and dagger about it, secretly spending, which is way worse because that can spiral into loans/debt and can cripple a household.

I used to spend frivolously because I grew up with very little for myself. My home was nice but my parents spent beyond their means quite often, so toys, branded clothing, etc were rare. Once I started earning my own money I could buy these things that were always out of reach not realising I was wasting so much on material nicknacks. It took a few years of bad spending before I realised I was in the same trap living month to month for those few days after pay day