Mount Whitney in California is the highest peak in the lower 48 United States. It's 14,494 feet high. You could probably fly to the top of Mount Whitney in about 15 minutes. To walk the same distance might take you 15 days. It could well be that flying to the top of Mount Whitney is a lot more fun than climbing it, but climbing will give you a lot more happiness because you'll have achieved something quite difficult.
Happiness is internal.
It becomes part of your essence. Learning Torah is the ultimate in deferred gratification. The Torah is as hard as steel and as difficult to grasp as water. There is no physical pleasure in this world that can compare with the ecstasy of cracking a difficult Talmudic idea. It may not be fun in the traditional sense, but it's the greatest happiness that there is.