Was Leonardo lazy? Hell no!
Was he an Artist? Sometimes. An inventor? Constantly it seems.
But all one has to do is follow the money: Leonardo was... a courtier. You know, on of those sychophants trying to entertain whatever prince was footing the bill. And these princes, well gee, they had some strange priorities.
So, Leonardo spent his time build water organs, planning the entertainment at parties, designing stage props and scenography for allegorical representations of whatever prince's virtues and victories (this symbolical stuff was actually politically important in the Renaissance).
Sure the princes were inetrested in war machines, but they were also interested in Whopping Big Statues of themselves. I.e. the case of the Sforza prince of Milan (forget his name). He hired Leonardo, who came equipped with his little drawings and a smashing plan for building sewers for Milan (might have cut down the death rate from colera etc.). Unfortunately all this Sforza guy wanted was a Massive equestrian statue, the biggest ever. So Leonardo spent several years sculpting models and trying to solve all the problems with casting bronze on a hitherto unparalleld scale. In the end nothing came of all this, not even that damn statue. But Leonardo certainly seems to have earned his wages.
This would also disprove the ADD-theory. (Which I would think is part of "the pathological school of history", the one speculating that Nietzsche's philosophy was caused by his syphilis and Wittgensteins by his supposed autism. And Napoleon lost his wars due to some very strange illnessess making his penis shrink, or so I've been told.)
As far as esoteric messages in Leonardo's paintings, they are full of them. However, they are nothing like the ones dreamt up by Dan Brown (who nicked it from Baigent, Leigh and Lincoln, who nicked it from Gérard de Sède, who was probabaly a dupe for Jean Cocteau's 1950's "pataphysical" art happening, the Grand Conspiracy Theory of the "Priory of Sion".)
No, Leonardo stuck to the "Hermetic" tradition that the renaissance knew and loved. (The idea that there was textual evidence of God's plan for Creation older than the Bible; the writings of the "Egyptian" Hermes Trismeghistos most importantly.) He wasn't alone in this. Botticelli's and Michelangelo's work were just as full of these references.
The reason Leonardo didn't pursue more of his ideas or paint more pictures, was simply that he was paid to do other stuff, but such that we have no trace of it or consider it trivial. IMHO a superb reason.
