Well you could just say "madness is akin to genius" ("...and other cliches...") and have done but that's dismissing him as a British eccentric. That's correct. Because he was eccentric.
He wouldn't get away with it today. He'd have the publisher breathing down his neck as soon as The Hobbit hit number 1 and he'd have had to churn out Lord of the Rings sharpish (we'd have had Trotter and so forth...). And then some more books too. He might not even have got it published at all as it might have been feared it was too 'mad'.
What breeds eccentrics in Britain in particular I think is the way we hate boastfulness, and with it, visible success. It's just vulgar and 'a bit chav' to show off how much money you've made, even if it is through honest hard work, and as a consequence, we do seem to like loafers more than strivers - we even have a splendid magazine called The Idler and a website dedicated to biscuits and cakes and teabreaks
http://www.nicecupofteaandasitdown.com/ Yes, even in the corridors of power you meddle with a civil servant's entitlement to a teabreak At Your Peril...and look how flustered Bilbo was when all those dwarves threatened to eat the tasty contents of his larder
So, with a culture that values the opportunity to sit and take a fifteen minute break morning and afternoon, a one hour lunch and six weeks' holiday we have time to ponder 'Stuff'. And that's why there are so many eccentrics.
Of course Tolkien did not have a whole lot of spare time until he was middle aged as with a large family in the pre-NHS era he had to work silly hours just to pay the doctor's bills, recording linguaphone lessons, marking school exams and setting exams for soldiers, and so forth. But he still wasted all that precious free time not in doing something 'productive' but in making up languages and poems about Elves.
That was all perfectly OK in Oxford of course, home to many eccentrics down the years, including Tolkien's contemporary the notorious Maurice Bowra, Professor of Poetry and Warden of Wadham - Tolkien is small-fry in the mad stakes in comparison, though in and of himself he was somewhat odd being a Catholic in a very CofE city and University. I've heard it said many a time that Oxford is a bit like a magnet for eccentrics.
And he used to smoke his pipe while riding his bike. What more proof do you need?
