Control is why. You can't give a plant 24hr light and boost your veg. growth with sunlight (it's dark at night).
That might actually sound feasible if grow lights put out equal amounts of light and as full range of the light spectrum as the sun. You grossly underestimate the intensity of the sun. Even on a cloudy day the sun can put more light on plants during hours of daylight than someone can with what would be like a birthday candle amount of light in comparison to the sun using a 24 hour light cycle.
It is true that it is dependent on what part/area/region of the world someone lives in. Some areas are not at all conducive to outdoor growing of even fast flowering strains. But if in an are that is conducive to outdoor growing, outdoor will beat indoor every day of the week and twice on Sunday.
It was mentioned that indoor plants have more trichomes, become frostier. Well, again that would depend on where someone would be growing outdoors. If in an area of high UV-B rays and or low humidity their outdoor plants will be as thick with resin-filled trichomes as fleas on an Alabama hound dog.
I live in the Southern U.S. and while I will not claim it to be the most optimal area for outdoor growing, when I grow plants in pots on my deck not all that long into flowering they look like we had an ice storm, they are covered with glistening trichomes. Very often even the large fan leaves will at least partially be thick with trichomes, and I am not just talking about White strains either.
There is no singular correct answer to the question is growing indoors or outdoors better because it all comes down to where someone lives. In some parts of the world a person will definitely be able do better growing indoors and in other parts of the world someone will definitely be able to do better growing outdoors.
Later, you cut back an hour or two from a normal full day's sun to force them to flower.
If you meant that when growing indoors you have the ability to flower at any given point of the year regardless of what the normal length of a day would be at that time of the year what you said would make sense. But comparing indoor growing to outdoor growing means you are growing outdoors during the normal natural outdoor growing season. That means days will naturally grow shorter and when the become 12 hours long or less flowering will begin. But at that point and time in the growing season that would be the; "normal full day's sun," as you put it. There would be no need or reason to cut it back any farther than that if growing indoors so your comparison or point is invalid. If you meant cutting the hours of light down to 11 or 10 hours, in most cases that would not cause any gain and instead create a loss. In the case of true pure equatorial sativas 11 hours of light and 13 hours of darkness is best, but few people grow true pure equatorial sativas. For everything else the additional hour of light will be a plus.
And again, later, you boost it back up to extra hours to pump up resin production near the end.
Since resin, and cannabinoids and terpenoids begin to be produced right after the formation of trichomes why would someone want to wait to attempt to increase resin, cannabinoid and terpenoid production until; "near the end" of flowering? Wouldn't it make more sense to attempt to maximize resin and cannabinoid and terpenoid production all through the flowering stage of growth?
Also, since anyone growing indoors with HID lighting will normally use a HPS bulb for flowering increasing the length of hours of light will not make much difference in the production of resin and THC. UVB light rays, something there are a lot of outdoors, are what cause increased resin production and THC production, and HPS lighting hardly puts out any UV rays at all.
If someone wants to; "pump up resin production" as much as they can indoors, if using HID lighting, they need to add MH lighting to their HPS during flower, 2:1 HPS to MH, or better yet add UV-B lighting during flower by adding reptile aquarium lighting to their HPS lighting and also keep their humidity level low, and it is senseless to wait until; "near the end" of flowering to do that and only gain a little when instead it can be done all through the flowering stage and more will be gained.
I never understand the mentality of some where they think the best way to grow, the best way to get maximum resin, cannabinoid and terpenoid production from their plants is to wait until; "near the end" of flowering and only then attempt to squeeze additional amounts out of their plants. Since these things have been proven to increase resin, cannabinoid and terpenoid production why, if say someone is growing a 10 week strain, would it make any sense to only do those things for the last week or two weeks or even three weeks when they could be done for all 10 weeks ... or if an 8 week strain, why only do them the last week or the last two or three weeks when instead they could be done for a full 8 weeks?
Do people actually believe that doing those things will only produce positive effect on plants; "near the end" of flowering and not all through the flowering period? If so, why?