From my observation, the main reason seem to be:
-Games no longer form long lasting communities to warrant such mods. Compare Bf42/2/2142 with the newer Battlefields
-Segwaying from previous, modern games, especially MP, have most of stuff happening on dev/publisher servers, "Always Online" and all that jaz, which in turn means they have to lock things down much tighter to fight of hackers, and in turn hurt modding
-The rise of ingame shops/DLC means that modding intervenes on their finances.
Almost no big AAA release from the past years have had a modding community grow around it, at least not a visible one. In fact, most modern AAA seem to be forgotten as fast as they are released.
I haven't been following modding in a while, but, Source 2 still isn't available to public, right?
That is quite telling of the current state of the industry considering Valve engines being major modding platforms for nearly 2 decades, having given life to some of the best TCs, singleplayer and multi. All 3 current flagships of Valve are uplifted mods, yet all they have recently done for modding is reduce it to skin gambling.
SunnyBittern
joined
Somewhat positive.