; it's not like anyone expected the series to be relevant again after it went untouched for over a decade
The interesting thing is plenty of people, even myself, have been saying that VALVe was holding off as they like to use Half Life as a showcase of new ideas. Half Life was proof that you could run the Quake engine on Windows 95 and be a popular game. Half Life 2 was all about the physics and facial animations (that to this day are still fantastic). Episode one was showing off their new AI for Alyx and Episode 2 is massive on the upgraded physics, hence the collapsing train bridge in the beginning.
Most games are built around those ideas for VALVe. Its not really a big surprise they are launching a VR main title to really show off a full fledged VR game.