A source of reliable angle-of-attack information is important for airplanes, as flight at an excessively-high angle of attack can cause the airplane to stall, which is generally considered to be an undesirable occurrence. To this end, airplanes generally have several redundant angle-of-attack sensors (usually consisting of vanes that stick out into, and align themselves with, the airflow, but sometimes using complicated pressure-sensing mechanisms instead) to provide warning of a dangerously-high angle of attack.
These sensors, however, are generally mounted on the forward fuselage, below the cockpit, which is not, for most airplanes, where high angles of attack actually cause problems. Where AoA matters is on the wings, which produce the lion’s share of the airplane’s lift and which need to be kept from stalling, and where the direction of the local airflow is not necessarily the same as that experienced by the AoA sensors on the forward fuselage. Exactly how not-same it is depends (as do quite a lot of an airplane’s aerodynamic properties) on the airplane’s airspeed, which is why readings from nose-mounted attack-angle sensors need to be adjusted to correct for the effects of airspeed, which is why (for instance) high-attack-angle protection on fly-by-wire Airbusses is inoperative in the absence of valid airspeed data.
Mounting the angle-of-attack sensors at the airplane’s wing roots, rather than beneath the cockpit, would allow the AoA to be measured directly right where it counts, eliminating the need to correct their readings for airspeed and allowing accurate attack-angle measurement even without any airspeed information at all, so why do most airplanes still have their attack-angle sensors on the forward fuselage instead of the wing roots?