Chlorination of Propane
The reason might be one of kinetic versus thermodynamic control.  The actual halogenation step is stage 2 in this scheme:

(reaction scheme from chem.libretexts.org)

The 2-radical might well be more stable, but that doesn't mean that it will react faster than the 1-radical.  If the reaction rate constant for the 1-radical with chlorine is much faster then the 1-chloro- product will predominate.

More likely, though is that it is that the 1-radical is formed in preference over the 2-radical in step 1. The halogen can attack at one of three positions, so statistically speaking you'd expect more 1-radical over 2-radical intermediates.  If this species then reacts immediately in step 2 without rearrangement then you'd get a predominance of the 1-product formed.
(Thanks to Karl for pointing this out).