It only came out on DVD around 3 years ago, due to fan pressure.
I bought the whole box merely on merit of Amazon reviews. Haven’t regretted it, and I've watched it all two or three times. If you like subtle and funny animation for adults, I recommend it.
It was cheap too, less than fifty bucks for a handful of seasons. Eight DVDs, including two movies which came after the series, but stayed in continuity.
… hokey smoke, it’s down to 22 bucks! Unbelievable.