Without a one-off fee upfront?
1.You wouldn't recoup your time investment on each app for at least 2 years.
2.The upkeep with each of those apps during that time would eat up significant portions of your time.
3. If an app did go down for whatever reason the firm could choose to cancel your arrangement. If that happened in the first 12 months you'd really be sunk because you have no one else you can sell that app to.