Hans-Hermann Hoppe notes in an interview:

    among Austrian economists there has been some speculation why
Hayek's recognition came so late (in 1974). One highly plausible
explanation is this: If the prize is awarded for the development of
the Mises-Hayek business cycle, then as long as both Mises and Hayek
are still alive you can hardly give the prize to Hayek without giving
it also to Mises. Yet Mises was a life-long opponent of paper money
(and a proponent of the classical gold standard) and of government
central banking--and the prize money for the economics "Nobel" was
"donated" by the Swedish National Bank. Mises, then, so to speak, was
persona non grata for the "donors." Only after Mises had died in 1973,
then, was the way free to give the prize to Hayek, who, in contrast to
his "intransigent" master and mentor, had shown himself sufficiently
willing to compromise, "flexible," and "reasonable."

Update: A friend told me Friedman was in favor of Mises getting a
Nobel; I expressed disbelief, so he quoted to me from p. 353 of
Ebenstein's Hayek bio:

    Friedman has written in response to a query from Mark Skousen: "I
believe Ludwig von Mises was certainly of a quality that would have
made him an entirely appropriate recipient of a Nobel Prize" in
Economics (Friedman letter to Mark Skousen, March 5, 1996).

I don't get this. How can Friedman think this if Mises's methodology
was so much at variance with Friedman's positivism? See, e.g.
Friedman's comments, as quoted on p. 273:

    In 1995, Friedman made the following comments about Hayek's and
particularly Mises' methodological positions:

        I never could understand why they were so impressed [at LSE]
with the lectures that ended up as Prices and Production, and I still
can't. As of that point, he [Hayek] had not freed himself from the
methodological views of von Mises. And those methodological views have
at their center that facts are not really relevant in determining, in
testing, theories. They are relevant to illustrate theories, but not
to test them, because we base economics on propositions that are
self-evident. And they are self-evident because they are about human
beings, and we're human beings. So we have an internal source of final
knowledge, and no tests can overrule that. Praxeology.

        That methodological approach, I think, has very negative
influences. It makes it very hard to build up a cumulative discipline
of any kind. if you're always going back to your internal,
self-evident truths, how do people stand on one another's shoulders?
And the fact is that fifty, sixty years after von Mises issued his
capital theory--which is what's involved in Hayek's capital
theory--so-caled Austrian economists still stick by it. There hasn't
been an iota of progress.

        It also tends to make people intolerant. If you and I are both
praxeologists, and we disagree about whether some proposition or
statement is correct, how do we resolve that disagreement? We can
yell, we can argue, we can try to find a logical flaw in one another's
thing, but in the end we have no way to resolve it except by fighting,
by saying you're wrong and I'm right.

        On the other hand, if you take more like a Karl Popperian
approach, an approach which says what we do in science is to offer
hypotheses about the consequences of certain events and, if we
disagree, we test those by trying to seek empirical evidence that
contradicts our predictions--if you and I disagree, we have another
way to solve our problems, resolve our differences. I say to you, what
facts can I find that will convince you I was right and you were
wrong. You say to me, what facts can I find that will do the opposite.
Then we go out and observe the facts. That's how science progresses.

        Now, as I said, I believe that Hayek started out as a strict
Misesean, but he changed. The more tolerant atmosphere of Britain,
then subsequently of the U.S., and his exposure to a wider range of
scholars, led him to alter that position.

    Does this sound like someone who would respect Mises enough to
think he deserves a Nobel Prize?

Hoppe notes in another interview:

    A&K: Supposing you sat on the Nobel Prize committee for economics,
who would you consider deserves the Prize--please exclude yourself.

    HHH: Anyone of the leading lights associated with the Ludwig von
Mises Institute. However, the nominating committee is filled with
statists, and the prize itself has been established by the Swedish
Central Bank, and so, given the fact that Misesian economists are
uncompromising free-marketeers and oppose in particular any form of
monetary socialism (central banks), their chance of ever winning the
prize is virtually zero.

    A&K: Why would you nominate them?

    HHH: Because Misesian - Austro-libertarian - economists have the
best grasp of the operation of free markets and of the detrimental
effects of government (states) on the formation of wealth and general
prosperity. This is illustrated by the fact that Mises, and those
economists following in his footsteps, have by far the best record in
predicting the outcome of socialism, of the modern redistributive
welfare-state, and in particular of government-controlled paper-money
regimes and of central banking.