Because a stadium generates more income for its owners, whereas building 10,000 homes does not.
For the government, it's cheaper to have the poor on the streets than to build them houses. When someone has a lot of money, sometimes instead of donating it or spending it on luxuries, they prefer to acquire assets to generate more money. Let's say the stadium is an asset, so in the long term, it can benefit the owners and potentially recoup their investment, which wouldn't happen when building homes for the poor. Although honestly, I'm not sure if the homes could also be used as assets, as if people had the income to buy those 10,000 houses, it might generate profits.