Genetics is the primary factor. Some plants "can" grow donks, some cannot.
Take a plant that "can" and give it too many mouths to feed (colas) per sq ft relative to light and other environmental facotrs and you won't get donks. Donks are not necessarily the goal, but using this as a point of reference.
relative to any 1 plant you are working with, more colas per sq foot will results in smaller buds. There probably is an "optimal" bud size to maximize production for each particular plant, but anyone who things they can dictate that through pure trial and error of a handful of plants is absolutely insane. too many variables...
From what i've read in "dr photons corner" on cocoforcannabis website, 2.x per sq ft is ideal. No idea how they came to that conclusion and it certainly doesn't take into considerations all possible variances of relevant traits. I'm sure they makenote of that somewhere, too. That is one of the best sources for information i've found on the internet regarding marijuana.
Reading their post on defoliation/pruning should be required reading for all growers. Not just for teh topic at hand but the explanation of how a lack of evidence and a hypothesis is fucking useless on its own. LOL. Good deductive reasoning, understands why comparing to a control group is necessary etc etc.. just good stuff going on in terms of how they think and come to conclusions... rational, logical conclusions.. not bat-shit crazy nonsense of uninformed dopes that is simply repeated ad nauseum without any thought, let alone effort, of testing or verifying it. and, if they do try to test it, they often perform horrible experiements destined to give them the answers they prefer, lol, or just utterly useless methods - either way.. same thing results.. .nonsense.
Your plants look healthy but a heavy on sugar leaves. did you remove a lot of leaves at some point? This could definitely hinder flower growth. Unlike the common beleif, removing a shit tone of leaves indiscriminately is not going to have a positive effect on production.
leaf removal powers growth and not jsut in the local area where it connects to plant. avoiding risks of fungi an dother issues is a good reason to remove a leaf or two, but not a whole shit load.
if timed poorly, you'll end up with a shit ton of sugal leaves because the plant is trying to compensate -- this could just be a genetic trait too... can't be certain but mentioning it just in case.
maybe, too many "suckers" underneath canopy. reducing axillary growth below will improve bud formation up top, to some extent. but overall yield should be similar. it's a matter of propotion of larf that you can impact by pruning lower axillary buds off before flowers start developing in earnest. This isn't somethign you should do at this stage, though. 4 weeks in.. your vege growth is nearly abated if it hasn't already. the flower sites were being build over the last 4 weeks and this is probably too late to maipulate the resulting growth without costing yield significantly.
but, in the end, this plant probably doesn't produce donkey dick buds even if you do everything perfectly. it's relatively healthy, has a fairly full canopy... should be doing mostly fine relative to its potential. We don't impact the results nearly as much as people perceive. We have great sucess when we don't step on our own dicks or flaps (I'm trying to be gender inclusive, lol)
Keep it healthy. Keep it happy.. all you can do. Don't remove so many leaves next time. Even shileded leaves provide numerous benefits to the plant. They are never "suckers". they are value-added anatomy once they mature. Leaevs are only an energy-deficit bits the first few days as they develop and after that they only contribute energy for grwoth or perform other necessary functions like storage and transpiration/respiration -- transpiration is how it gets carbon, the most important buiklding block of all. So when you remove leaves you remove its ability to suck up carbon, too.. it's not just about receiving light. less carbon = less growth.