There really are too many techniques in grappling. It's just so easy to get bogged down with them. Judo on the other hand seems so simple. Although, that doesn't mean it's easy to throw an opponent because it isn't. Judoka seems to practice a handful of the same techniques over and over again. One kid I train with only does seio-nage and o-uchi now and again. It's said that many of the top players only use 2 to 3 throws. The rest is just body position, reading the opponent, athleticism, stamina and strength from what I can gather.
Jiu-jitsu on the other hand has so many guards, different passing methods and ways to submit an opponent that you need an encyclopedia brain to hold them. That or teach all the time. I suppose this is why it takes so long to reach black belt and why people get so addicted to it. It engages the mind more than the rules of Judo ever do.
I'm not knocking Judo though. I enjoy training it once a week now. I think any good grappler should be training in both. It's even made me consider trying drills judo-style with BJJ sweeps, etc. I'm also attempting to cut down to a core set of techniques only but maybe this is a side-effect of doing BJJ for almost 6 years now.
One thing I can say is that Judoka are very serious in their attitude here in Japan and reflect the society in its nose-to-grindstone no nonsense attitude while BJJ takes a relaxed approach and practitioners tend to smile and laugh a lot more than their Judo counterparts. Perhaps if Judo in Japan were a bit more forgiving and fostered an enjoyable atmosphere more kids, like my own son, would practice it.