Itaewon class?

I'm watching this K drama on Netflix and I don't understand a few things.

Saeyori has invested high value stocks in the Jangga company and plans to ruin them. But what does he get when the company is broke? What does it do for him?

He wants revenge. Jang Geun-won is the son of the chief of Jangga and also the one who killed Saeroyi's father. He has also been kicked out of school because of Jang Geun-won and Jang Dae-hee, and therefore has no degree. He also went to jail for Jang Geun-won and was therefore no longer able to become a police officer, so he destroyed Saeroyi's dream.