The key is small. Owning and operating a small business takes money and time - both of which are limited. Theoretically, with $10m, you could start 10 $1 million businesses (say 10 restaurants). However, you would have to hire additional people to oversee each business which is okay if you open the 10 restaurants serially as opposed to concurrently (open one, make it a success, hand it off to a trusted and trained manager, open a second, etc.). Assuming 2 years to establish one business, that's 20 years and you would have been better off if the first restaurant was successful to start a franchise.
Most small business owners cannot or do not want to put in that amount of time.