But does anyone design their scenarios or campaigns around a particular theme?
No and yes.
No: in dramatic/thematic play, I prefer the theme to emerge from the way the players build and play their PCs in the context of the system. Some systems are better at this than others.
Yes: I prefer RPGing which is theme-laden.
Some of my terminology for thinking about this is taken from Robin Laws's Hamlet's Hit Points:
https://gameplaywright.net/books/hamlets-hit-points/:
* The fiction is procedural if it concerns "a protagonist’s external or practical goal";
* It is dramatic if it "invests us in the protagonist’s inner goals".
Dramatic fiction tends to be theme-laden by default, I think - the inner goals bring emotional resonance with them. Procedural fiction becomes theme-laden if the external or practical goal suggests something beyond it of emotional or symbolic. significance (eg blowing up the Death Star).
Examples:
* In a Rolemaster game, one of the PCs became addicted to a magic-enhancing drug. This led to a downward spiral of financial and social ruin. Overlapping with this, the system produced a series of big failures for him, which compounded his suffering. This moved from the procedural to the dramatic when the character had to make compromises with another PC, and agree to betray his city, in order to get healing for his addiction and support to overcome his other problems. The character achieved a degree of redemption when he fell in love with, and established a relationship with, a NPC. Then she was killed when one of the demons controlled by the other, formerly dominating PC , ran amok; this provoked a new spiral into bitterness and disregard of personal wellbeing.
* In another RM game, I (as GM) did set up situations to deliberately bring out a particular theme: inspired by Wagner's Ring Cycle, and adapting some AD&D and 3E D&D scenarios, I established a situation where the players had the opportunity to have their PCs step outside the cosmological boundaries that the gods had set for themselves, so as to help a trapped, "dead" god for whom they had developed an affection, and find a new solution to the problem of holding back an ancient evil. The action was predominantly procedural, but it reflected the PCs (and their players) rejection of karmically predestined outcomes, and in the climax of the campaign they came up with a series of novel solutions to their cosmological quandry, which satisfied the sentimentalist in me: the paladin PC, who had been willing to take the place of the trapped, "dead" god in holding back the ancient evil outside of space and time in the Void, was able to have a karmic duplicate of himself take on that role, while he retired to establish a monastery for training devotees of the dead god on the island which was the (stone) "body" of the "dead" god on earth; and another player brought his PC's romance subplot (wherein he had wooed a sorcerer the PCs had rescued from a demon) to a resolution, solving the problem of the inevitable exhaustion/corruption of an eternal guardian by having his family's generations bear the responsibility of guardianship instead, with hope and energy thus being renewed with each generation.
* In my 4e game, the players built their PCs following the defaults in the PHB (and later the other player-focused books) but I added two extra requirements: that each PC must have one loyalty to something or someone; and that each must have a reason to be ready to fight Goblins. By following and building on the players' leads, and their interplay with the default cosmology and thematic logic of 4e, the game evolved from a conflict against slavers and an attempt to reach peace with the Goblin raiders; to a thwarting of the demonic ambitions of Gnolls and cultists; to journeys in the Underdark in which the PCs brought ruin on the duergar, and killed Torog; to the sealing of the Abyss, the killing of Orcus, the liberation of the Drow from Lolth, and the (at least temporary) staving off of the Dusk War. Life and death, pragmatism and duty, and chaos vs law were the recurrent themes here in a predominantly procedurally-oriented game.
* I am a player in a (slowly) ongoing Burning Wheel game. The basic orientation of play is determined by my PCs Beliefs and relationships and similar character-establishing elements of the PC. For my paladin-esque PC, he has had key opportunities to establish his commitment to upholding the values of his order and redeeming his family; this action has been a mixture of the procedural and the dramatic (for instance when he burned the letters he found in an evil wizard's tower that very strongly implied the wizard was his mother's father). So far it is his sorcerer sidekick who has actually travelled further along a purely dramatic arc, as she started out motivated by a mixture of fear and somewhat bitter resentment, but through events has been able to realise herself as more self-assertive, more respectful of my PC, and ready to assist in the cause of liberating his homeland. My friend who GMs this game has never GMed before, but is very skilled at using the material and techniques that Burning Wheel provides, and following the leads I provide in the play of my PC and his sidekick.