GTA IV had a scene. Not as large as San Andreas before it or V after it, but a scene nonetheless. The reasons why are fascinating and paint a picture of why OpenIV - the cornerstone of the V scene - originated in this generation.

Why the IV scene was smaller

Late PC port. GTA IV was released for PC in December 2008, eight months after consoles, but the port was notoriously rough. Performance problems hindered the modding community's growth.

Different file format. The RAGE engine brought new packed-archive formats (.RPF files) that required reverse-engineering. The community got them figured out, but it took longer than expected.

Smaller modding community at the time. Modding culture wasn't as big a part of PC gaming in 2009 as it was by 2015.

What IV nonetheless built

OpenIV. The foundational tool for every modern GTA modding project started here. If it weren't for GTA IV's modders working with the .RPF format, you wouldn't have OpenIV's extension for GTA V today.

ScriptHook. The script-modding framework that ScriptHookV grew out of originated in IV's era.

MultiTheftAuto-style frameworks attempted IV multiplayer, but never to the extent that SA-MP did. RAGE Multiplayer's later success began with foundations laid in the IV era.