They both fly. They both carry loads.
Why do cruise missiles look too different from subsonic jet aircraft?
They are designed to fly at one Mach-altitude combination only. Regular aircraft have to take off and land (low Mach, low altitude) and cruise (high Mach, high altitude). Cruise missiles are launched either from aircraft or accelerated by a booster rocket so their flight starts at a high Mach number already. Next, their nap-of-the-earth flight means they never go high, but stay low for the whole duration of the flight.
To minimize wing surface and, consequently, drag, the cruise missile has a higher wing loading than any aircraft. The published data only gives mass and wing span, so I needed to guess the wing area:
For comparison, a typical airliner wing loading is around 600 kg/m², which is also the maximum wing loading of the B-52. Using Wikipedia data, the maximum wing loading of the B-1B is even almost 1200 kg/m², but the published area is for the outer wing only, linearly extended to the center. If the large delta is added, the wing loading drops below 1000.
At the other end of the scale, typical glider wing loadings range from 30 kg/m² (without water ballast) to 55 kg/m² (with full water ballast). A typical GA airplane with a stall speed below 61 knots has 60 kg/m² to 70 kg/m², a TBM-700 can reach up to 180 kg/m² while jet fighters range between 300 kg/m² and 500 kg/m².
Next, the cruise missile needs to be stored, so it must be compact. In case of the Tomahawk, it is designed for the 21 inch torpedo diameter standard. The AGM-86 is mounted on a rotary launcher, and the trapezoidal fuselage cross section makes most use of the available space. Since it never needs a runway, the foldable fins can be arranged symmetrically for best control effectivity and to avoid cross coupling between yaw and roll. For maximum range the cruise missile stays out of the transsonic speed regime, so little to no wing sweep is needed. In the end, cruise missiles have a very straightforward and functional design.
AGM-86 on rotary launcher (picture source)
Airplanes are expected to land, refuel, and be reused.
Missiles are not expected to have the same life-cycle.