How does it make sense that because I do not have cargo space that I cannot still take a mission that is only offering that cargo as a reward? This does not make sense in either a game sense or a business sense.
It's been mentioned 1,000 times, not sure why FDev haven't doen anything about it (don't recall it being in 2.4's patch notes either). It will likely change in future, the question is, when.
It is a requirement to make sure you have the room to put it when you get it. Because we don't get pad deliveries as would actually happen in a 'real world experience'.
A ship in a port gets deliveries to the dock. Not to the ship. The crew of the ship load it onto the ship from the dock.
In the future though, the whole system may be automatic and so there is no need to handle things. They get auto loaded through some mechanism thus you would need to have the room for it as a reward. The alternative would be to change it so you have to have the room for the reward to turn in the mission. Meaning you will never see it for turn in until you have cargo space as other missions with rewards like that. Passengers giving cargo won't let you unload them till you have room.