They would only do the deal on the spot if that was their only option. But they have the option of spending $0 and having the majority of the users moving to the official app.
If Apollo's userbase was actually generating $20mm/yr, acquiring Apollo for $10mm is a no-brainer. But if that were the case, keeping Apollo running as it is would also work.
Obviously this is not the case. Apollo is confusing costing $20mm with generating $20mm.