It isn't technically classed as a legacy device, more a low activity one. If you compare the development of this phone to something like the Z then there is a lot less activity.
If people created more custom ROMs, ports, apps, mods etc which would boost activity. Also CWM for locked bootloaders would allow for said activity to be greatly improved.
Sent From My C1905
My Phone: Sony Xperia M C1905 | ROM: Modified Stock | Base Firmware/Build Number: 15.4.A.0.23 | Android Version: 4.3 | Kernel: Stock (Permanently Locked Bootloader) | Network: GiffGaff
My Tablet: Google Nexus 7 (2012) | ROM: CM11 | Base Firmware/Build Number: 11-20140527-NIGHTLY-grouper | Android Version: 4.4.4 | Kernel: CM11 | Network: N/A