Earlier quoted context omitted.
None of the "blank" games are Valve's IPs but acquisitions which kind of stopped in development or releases after Valve acquisition. Half-Life was their last original IP and even that ended in a complete cliff hanger with Episode 3 or sequel nowhere to be found. It seems that Valve has serious problems actually pushing their games to completion since they started printing money with Steam and pressure to actually rel…
> None of the "blank" games are Valve's IPs but acquisitions which kind of stopped in development or releases after Valve acquisition. TF2, CSGO and Dota 2 are regularly, and visibly updated constantly. In no way are these moribund or 'stopped in development'; the latter two are still among the most played and watched competitive games online. It's also stretching things to say that Valve 'acquired' Portal and it was…
Left 4 Dead, company was bought.
Team Fortress was a Mod for Quake. Through a aquire hire transfered the Mod to Half Life 1 (GolgSource engine based on Quake 1 engine). Team Fortress 2 was planned to be released in 1999/2000. Though it took additional 11 years and at least complete restart to release Team Fortress 2 based on Source engine.
CounterStrike was a free Mod from fans for Half Life 1. They aquirehired the team around CounterStrike 0.9. Some say it went downhill from there. CS 1.4 was the last classic CS.
CS Source was a port from GoldSource to Source engine. As Source engine is just an incremental evolution, it was just a matter of building the game again and later replacing textures and models with higher ones, etc.
CS Go is a rehash of CS Source simplified for console gamers and ported to consoles.
Dota was originally a fan-made Mod to WarCraft 3. Valve aquirehired them to create Dota2, a standalone version based on Source engine. Blizzard wasn't amused and announced a similar game a few days after Valve announced Dota2 back then.
Half Life 1 (GoldSource) is based on Quake 1 engine (with small parts from Quake 2 engine), and of cource evolved. Half Life 2 (Source engine) evolved from GoldSource engine. Videos from HL2 beta show clearly the old DX7 renderer and loading older HL1 map format. Valve worked on HL2 episode 3 and Warren Spector (Deus Ex, System Shock) and his former company worked on HL2 episode 4. But Valve decided to shut down both. The unclear situation for several years makes HL fans angry. HL2 episode 3 / HL3 is the new Duke Nukem Forever, at least that one got released after 11 years - we will see about HL2. We all remember also the shitshow around the HL2 release. The infamous HL2 demo at E3 2004 was faked and the game was nowhere to be ready. The leaked video footage a year later showed how far behind Valve was behind the announced release schedule. Half Life 2 was finally released another year later with heavily shortened gameplay and many previously features removed. Making it basically a different game that feels very differently to the original Half Life 1.