IIRC, that's not really the case.
Smea's Ninjhax (with Cubic Ninja) and Ironhax (with Ironfall) only exploit the 3DS "user mode", which allows a person to play game cartridges region free and run unsigned code like homebrew on their systems. Finding a user mode exploit requires finding a vulnerability in a 3DS game or software. In user mode, you don't have complete access to the 3DS hardware, as the games and applications you run are limited by the 3DS's underlying operating system (the kernel).
To gain full access to the 3DS hardware, allowing you to perform many activities including using custom firmware and installing CIAs (the Home Menu software on the SD card that you normally get from the eShop, this can either be homebrew or pirated games, or even 3DS cartridge backups you convert into CIA for installation on your SD card), you need to find an exploit to gain "kernel mode" access. Finding a kernel mode exploit involves finding a vulnerability in the 3DS operating system or the 3DS hardware itself, and this can be a lot harder to find.
Just because a system is hacked for user mode does not mean it has a kernel mode hack. Only 3DS firmware 9.2 or below has a kernel mode hack currently available. All 3DS versions support a user mode exploit with Ninjhax, but now with Ironhax, it's just an easier way to gain user mode access without paying for Cubic Ninja, and with a game installed on the SD card (instead of on a cartridge).