Why are fermionic atoms less prevalent than bosonic ones? Many atoms have no stable fermionic isotopes. Those that do typically have more stable bosonic isotopes than fermionic ones. Furthermore, the fermionic isotopes of most atoms are lower in natural abundance than the bosonic isotopes.
I would be grateful if anyone could explain why this is.
 A: An atom's symmetry under exchange is the product of its proton, neutron, and electron symmetries.  A neutral atom has an equal number of protons and electrons, so a neutral atomic is fermionic if its neutron number is odd, and bosonic if its neutron number is event.
Because of nuclear pairing effects, a nucleus with a given mass is most stable if its neutron and proton numbers $N,Z$ are "even-even." Nuclei which are "even-odd" or "odd-even" are less tightly bound than their even-even neighbors on the chart of nuclides.  So-called "odd-odd" nuclei are strongly disfavored, because they can transition to an even-even nucleus by beta decay, positron decay, or both.  There are only a handful of odd-odd nuclei which are found in nature. About four low-mass nuclei (deuterium, lithium-6, boron-10, nitrogen-14) are actually more tightly bound than their even-even isobars. A handful more (such as potassium-40 and vanadium-50) have decays which are forbidden for reasons of angular momentum, so their decay lifetimes are long compared with the age of the Earth and they occur in ores.
If you look at a chart of nuclides, the even-$Z$ rows have big stripes with lots of stable isotopes, but the odd-$N$ members are less likely to be stable than the even-$N$ members.  The odd-$Z$ rows tend to have just a few stable isotopes, with even $N$.
A: Elements tend to be more stable when they have an even number of protons and an even number of neutrons, because they can form pairs inside the nucleus. If you have an nucleus with an odd number of protons and electrons, you can reduce its energy (and thus its stability) by converting the unpaired proton/neutron (whichever unpaired one is at the highest energy level) into a neutron/proton.
Elements with an even number of both tend to be more stable than elements with an even number of one and an odd number of the other, which are in turn more stable than elements with an odd number of both.
If you want to read more about this, it is the "pairing term" in the semi-empirical mass formula.
