GTA IV had a scene. It just wasn't as big as San Andreas before it or V after it. The reasons are interesting and they explain why OpenIV - the tool that defined V's scene - came from this era.

Why the IV scene was smaller

Late PC port. The PC version of GTA IV launched in December 2008 - eight months after console - but the port was famously rough. Performance issues throttled the modding community's growth.

Different file format. RAGE engine introduced new packed-archive structures (.RPF files) that needed reverse-engineering. The community got there but it took longer than expected.

Smaller mod community at the time. Modding culture was less central to PC gaming in 2009 than it became by 2015.

What IV nonetheless built

OpenIV. The tool that would underpin every modern GTA modding effort started here. Without GTA IV's modders working on the .RPF format, OpenIV's later GTA V extension wouldn't have been possible.

ScriptHook. The script-mod framework that became ScriptHookV started in IV's era.

MultiTheftAuto-style frameworks attempted IV multiplayer but never matched SA-MP's scale. RAGE Multiplayer's later success traces back to IV-era foundations.