Granted the window between 3.0 and 3.1 for workgroups was a crappy period for networking but by the time OS/2 3.0 came out, it was already too late. And it's TCP/IP was that horrible dialup centric POS, nothing multi-homed, or with physical network cards.
in the OS/2 1.x there was a clear leader in the LAN, and it was Netware. But IBM just thought OS/2 should be as crappy as MS-DOS, and let the 3rd parties come along and add in support. Instead they should have at least bundled in LanMan support, but of course that would have killed a part number.
Windows for Workgroups 3.1 did have a network stack, and it was greatly improved in Windows for Workgroups 3.11. NT 3.1 came with TCP/IP, IPX, and support for SNA out of the box in 93. Warp was in '94.
The real 'killer' of course was Win32s+Winsock which gave us Mosaic. And why was IBM not killing themselves to make a Mosaic port to OS/2? Once people saw a graphical Internet, everyone I saw around me was clamouring for it, and it was amazing at the time how many Windows 3.1+Win32s+Mosiac installs talking to various UNIX dialup accounts using SLiRP. Something that was really unstable on OS/2, so more of the OS/2 fans were either going to Linux or to NT 3.5/3.51