  The spin of a newly formed black hole (BH) at the center of a massive star
evolves from its natal value due to two competing processes: accretion of gas
angular momentum that increases the spin, and extraction of BH angular momentum
by outflows that decreases the spin. Ultimately, the final, equilibrium spin is
set by the balance between both processes. In order for the BH to launch
relativistic jets and power a $ \gamma $-ray burst (GRB), the BH magnetic field
needs to be dynamically important. Thus, we consider the case of a magnetically
arrested disk (MAD) driving the spin evolution of the BH. By applying the
semi-analytic MAD BH spin evolution model of Lowell et al. (2023) to
collapsars, we show that if the BH accretes $ \sim 20\% $ of its initial mass,
its dimensionless spin inevitably reaches small values, $ a \lesssim 0.2 $. For
such spins, and for mass accretion rates inferred from collapsar simulations,
we show that our semi-analytic model reproduces the energetics of typical GRB
jets, $L_{\rm jet}\sim10^{50}\,\,{\rm erg\,s^{-1}}$. We show that our
semi-analytic model reproduces the nearly constant power of typical GRB jets.
If the MAD onset is delayed, this allows powerful jets at the high end of the
GRB luminosity distribution, $L_{\rm jet}\sim10^{52}\,\,{\rm erg\,s^{-1}}$, but
the final spin remains low, $ a \lesssim 0.3 $. These results are consistent
with the low spins inferred from gravitational wave detections of binary BH
mergers. In a companion paper, Gottlieb et al. (2023), we use GRB observations
to constrain the natal BH spin to be $ a \simeq 0.2 $.
