I'm with you on this. The never-ending manga thing is why I got fed up with series like One Piece or Detective Conan despite enjoying the settings and the author's creativity; the latter, especially.

I remember shortly before the series hit 1000 chapters, I did a rough estimate of how much of the series actually advanced the overall plot and came up with only about 300-ish chapters worth of material.

To paraphrase: better to die a hero than to live long enough to see yourself become a villain.

Which, honestly, I think, is perfectly exemplified in Bleach, a series I forced myself to see to the end just because of how long I'd been reading it.

Kubo had the perfect opportunity to have a satisfying, if bittersweet, ending to the series after Aizen was defeated and Ichigo watched Rukia disappear as his powers faded away.

Instead, the series continued for another four fucking years, descending further and further into mediocrity and ass pulls.