Because they literally don't care. As long as their OS is passable, they will keep the lion's share of the market. They have more money than most governments, and their headquarters is a giant city, with hundreds of buildings, a shopping mall, a bank, a soccer field, restaurants, hair salons, etc. They would have to do way worse for it to actually impact them. Their code is dozens of years worth of bugs stacked on top of bugs, and they just keep chugging right along, printing money.