TLDR is below.

As many people are aware that mission crew skills do not always provide the mission type that they want. The reasoning for this is to give a time sink for crafters and to not create a giant influx of resources on the GTN.

Note that this happens with all crew skills (not just UWT or diplomacy). It is noticed the most with UWT and diplomacy because uwt has 3 types of missions that rotate through and diplomacy technically has 4 (with dark/light medical supplies and gifts).

Each mission type has a respawn time which is higher than the mission time (when used repeatedly). On UWT you will notice that if you spend so much time sending out companions on fabric missions you will then start getting more and more gift/metal missions. If you send out companions on only companion gift missions eventually those will go away and will pop up with more metals/fabrics.

Diplomacy is unique in my opinion because it has the same rotation pattern but it also throws in alignment choices as well. So if you are only sending out dark side missions eventually your mission list will consist of only light side missions. If you only send out medical supply missions you will only get companion gift missions. If you only throw out dark side medical supply missions then eventually you will only have light side gifts.

The same thing occurs with other crew skills as well, i notice it on scavenging a lot when im farming for laminoid/aluminium which are level 1 compound/metals. if you send out a bunch of metal missions you willl eventually get a lot of compound missions and vice versa. On Archaeology, if you send out a lot of power crystal missions, you will get more artifact missions and color crystal missions; sending out more color crystal missions will net you more power crystal missions.

You can refresh the list by loading into a different zone by going planet hopping, or by logging out and back in. This system is put in place to not allow too many resources of one type from being generated so in a way it does control the supply of resources to a limited degree.

TLDR: mission availability is dynamic, they respond to the number of times they are sent out. Send more of one type out and you receive less of that particular type of mission.

That analysis is somewhat flawed.

I can run Rich level 5 lockbox slicing missions all day long with no problem getting both to spawn. If your theory were correct, those would vanish and be replaced by something else.

On the other hand, when I try to get Dark Side medical missions for Diplomacy, I can spend half an hour or more running in and out of my ship before something other than companion gifts or LS missions will appear. Very often, I can have 4 of 5 missions, and at times all missions, be LS gift missions, despite not having run any DS missions at all. Makes crafting on my Biochem largely a waste of time, as I cannot get the materials needed short of paying exorbitant prices on the GTN.

Diplomacy seems to be close to 90% gift missions, regardless of alignment, but that too is a flawed perception, as not everyone will have the same results. A quick look at my Diplomacy character shows exactly one medical supply mission out of 15 total available in the three ranks I can use. All of the rest are for gift missions. Sadly this is the rule more than the exception for me, but again, is likely not the case overall.

Personally I'd like to see the gift missions nerfed to about half of what they are now. I find them to be largely useless, both for leveling the companions, and as fodder for the GTN. More often than not they end up on a vendor for lack of anything to use them for. I don't even run the gift missions any longer. They're a wate of time and credits just to toss the gifts at a vendor at a loss, especially since you don't need them to advance companion affection.

It does make you wonder though, if they've not completely destroyed certain skills through sheer neglect and incompetence. The crafting system for this game has always been contentious, and their reasoning for nerfs, stealth or otherwise, have always been a bit vague.

I've pretty much given up on having implants, etc.. for my characters from Biochem. Several of the gathering skills are so badly broken that crafting in this game has become more of a chore than it's worth.

Yeah UT trading is the same doesn't seem to be any kind of pattern to it i mainly get moderate ones takes forever to get the others and i run gift missions as i thought it worked this way to but it seems completely random.

I would also like to see the gift missions nerfed as there's always tons of rich ones but i only use one companion the rest are just for skills.

Each mission type has a respawn time which is higher than the mission time (when used repeatedly). On UWT you will notice that if you spend so much time sending out companions on fabric missions you will then start getting more and more gift/metal missions. If you send out companions on only companion gift missions eventually those will go away and will pop up with more metals/fabrics.

This is easily proven false as very frequently as soon as a mission is finished you can send a companion back out on the same mission.

That being said, a significant part of Diplomacies problem is it is *still* broken from when they went through and divided the missions up republic side vs. imperial side based on the flavor text. IIRC for grade 4&5 there ARE no rich (and possibly bountiful?) medical supply missions for the empire. And vice versa for the republic for grade 3. However, I believe both sides get all the gift missions, so for diplomacy, at least, IIRC there really ARE a lot more gift missions available in the random pool.