Discs opened a lot of doors and benefits that weren't possible on cartridges– most notably imo is soundtracks and audio. Was a huge boost to the epic-ness of games.
I guess I never felt that games were not epic to begin with - also, I generally like chip tunes equally as much as non-chiptune CD audio.
I definitely get what you mean, though - It's true that CDs allowed for a LOT more data storage that obviously resulted in some advancements in video games as a whole.
Looking back, though, I don't necessarily enjoy larger, disc-based games more than I enjoy cartridge based games. If anything, cartridges also led to innovation within the limitations of the medium.
As for my reasons, its a combination of the direction towards digital becoming more prominent, my two favorite gaming franchises ever latest entries being big let downs back to back and the types of games or genres that I really enjoyed not getting made much anymore compared to prior generations.
I do feel certain aspects of gaming have become stale, but I wouldn't say is the exact or main reason for my decrease of enthusiasm for this hobby. The most fun I've ever had in a gaming generation (the 6th) was after the transition to 3D so I feel we differ in that front.
I think my reasons also include your reasoning as well - I'm not a big proponent of digital games - or DLC for that matter, and I really miss a lot of genres that either barely exist or just aren't producing as innovative games as previous gens. Shmups are a good example of the latter.
About disc based games - I very much enjoyed the 6th gen, and it was probably the last gen I completely enjoyed.
This may be hyperbole, but I truly do feel like we're on Gen 7, part 3 now.
We've had very similar experiences to that gen for the past 13 years, and I don't really see that changing any time soon.
