For example for Office365 Home you get 5 licenses including 1TB of OneDrive all for $99/year.
If I had to pay for just one Office Suite License(word, ppt, excel) would be around $200(low end). If I needed 5 that would be $1000. Now divide that $1000 over how many years you would probably use before wanting upgrade which for me would be 3-5. At 5 years it is average $200/year for lesser product because it doesn’t even include the value of 1TB OneDrive.
Thus 99$/year is cheaper in my mind and I am happy to pay them instead of looking for for some pirated version. It just works and I get newest version whenever it is released.