There are many applications that provide access to the Blockchain, but the vast majority are dedicated to workstations and other desktops or laptops. Indeed, these are so-called "heavy" applications, because the resources needed to operate the Blockchain are important: disk space (several gigabytes), network bandwidth (these gigabytes can be downloaded ...), memory, CPU ...
The advantage of Apidapp is to build a decentralized mobile application, which interacts directly with a Blockchain, and not through an intermediary that would relocate access to Blockchain on a server, in the Cloud.