What features would that be that changes the volume aspect completely from mATX for example? There is no reason besides volume on why a mATX board should be cheaper than a mITX.
The short version is simply low sales. Something we already know.
OK lets see,
Prices from Newegg (no AR, pure prices only)
For the same price the FM2+ board offers more features and you can also OverClock any FM2+ APU (Unlock or not through buss speed).
So by your logic, the Intel motherboards offer less features at the same price as AMD because Intel boards sell at lower volumes ???
ASRock FM2A88X-ITX+ = $83,99
Memory
Memory Standard
DDR3 2400+(OC)/2133/1866/1600/1333/1066
Maximum Memory Supported
32GB
Storage Devices
SATA 6Gb/s
6 x SATA 6Gb/s
SATA RAID
0/1/5/10
Onboard Audio
Audio Chipset
Realtek ALC1150
Onboard LAN
LAN Chipset
Qualcomm Atheros AR8171
Max LAN Speed
10/100/1000Mbps
Wireless LAN
WiFi IEEE 802.11 a / b / g / n
Bluetooth
Bluetooth 4.0 Class II
Rear Panel Ports
PS/2
1 x PS/2 keyboard/mouse port
Video Ports
1 x D-Sub
1 x DVI-D
HDMI
1 x HDMI-Out
1 x HDMI-In
USB 3.0
2 x USB 3.0
USB 1.1/2.0
4 x USB 2.0
eSATA
1 x eSATA
S/PDIF Out
1 x Optical
Audio Ports
5 Ports
Internal I/O Connectors
Onboard USB
2 x USB 3.0 + 4 x USB 2.0
Other Connectors
1 x Chassis Intrusion Header
1 x TPM Header
1 x CPU Fan Connector (4-pin)
1 x Chassis Fan Connector (4-pin)
1 x 24 pin ATX Power Connector
1 x 4 pin 12V Power Connector
1 x Front Panel Audio Connector
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GIGABYTE GA-B85N Phoenix-WIFI = $84,99
Memory
Memory Standard
DDR3
1600/1333
Maximum Memory Supported
16GB
Storage Devices
SATA 3Gb/s
1 x SATA 3Gb/s
SATA 6Gb/s
3 x SATA 6Gb/s
mSATA
1 x mSATA 6Gb/s
Onboard Audio
Audio Chipset
Realtek ALC898
Onboard LAN
LAN Chipset
Intel
Max LAN Speed
10/100/1000Mbps
Wireless LAN
Wi-Fi 802.11 a/b/g/n/ac
Bluetooth
Bluetooth 4.0, 3.0+HS, 2.1+EDR
Rear Panel Ports
PS/2
1 x PS/2 keyboard/mouse port
Video Ports
1 x DVI-I
HDMI
1 x HDMI
USB 3.0
2 x USB 3.0
USB 1.1/2.0
5 x USB 2.0
S/PDIF Out
1 x Optical
Audio Ports
5 Ports
Antenna Connectors
2 x Wi-Fi antenna connectors
Internal I/O Connectors
Onboard USB
2 x USB 3.0 + 2 x USB 2.0
Other Connectors
1 x 24-pin ATX main power connector
1 x 4-pin ATX 12V power connector
1 x CPU fan header
1 x system fan header
1 x front panel header
1 x front panel audio header
1 x S/PDIF Out header
1 x serial port header
1 x chassis intrusion header
1 x Clear CMOS jumper