As documented in wikipedia Endian is fork of IPCop. This is true for IPFire also. Therefore the resamblance.
If I remember right, the fork was aiming a commercial solution from beginning.
The IPFire fork always was real open source solution. Business interests are only in HW puchase and paid support plans by Lightning Wire Labs ( Michael Tremer ). In my experiance this drives open development more than the partially closed solution of Endian.
Yes, I knew they both are based on IPCop, I just had the suspicion they silently switched to IPFire. But I guess that would be visible in the source files.