hmm ok you kinda picked up on one of the reasons why.
Outdoor ussually only gets about 8 hours direct sunlight a day, it might even be less if its in someones backyard, a forest, or near mountains. This make the plants grow more leaves, so you get leafy bud, with a large of amount of space between flowers on the stem. Obviously this has a lower value.
A lot of outdoor grows are poorly tended to, and males are not removed from the crop, so you end up with 100+ seeds in every ounce. When ive seen bags like that, 1/4 or more of the ounce's weight is seed.
dont get me wrong some outdoor can be great if it gets stacks of light and is well looked after. The best combo would be plant under sun all day then move it inside under a lamp for remainer of light cycle. the sun is the best grow lamp.
outdoor is more susceptible to frost, insects, and being found, but indoor is susceptible to mold/fungus, and other problems from poor ventilation like leaf curl/burn.