[MENTION=23751]Maxperson[/MENTION], your Corellon wanting a message delivered was an excellent one for acceptable small obligations. There is a lot of potential flavor there. It's a nice reminder for the player(s) about the patron, and that could lead to a lot of interesting plot hooks. And without knowing more about what [MENTION=22779]Hussar[/MENTION] describes in this Background system, that may apply as Background.
However, I would say that the underlying problems within this warlock/patron discussion pertain to two interrelated issues: (1) PC-GM Cognitive Dissonance, and (2) Player Micromanagement.
In the case of (1), the player may have come to the table with a particular conception of who their patron is, the nature of their patron/protegé relationship, and what their patron means to them. (And they may be under the impression that the GM understands this as well.) In play, however, the GM may then dictate/impose a completely different understanding of that relationship or patron on the player. It may defy the PC's backstory. It may defy their sense of character. Not in a way, however, that challenges or grows that sense of character but in a way that contradicts or "retcons" it. If the dissonance is too great, the player may abandon their character entirely because "frak this junk; this is not what I came here to play." In a more freeform game like Fate, I could change my character aspects to something more appropriate as a result. But for a class-based game like D&D, pushing a player out of that class that they may otherwise enjoy playing can be ruinous for their experience.*
In the case of (2), many players dislike the GM micromanaging player characters through their deities/patrons/alignment/etc. So the desire to lockdown the patron as Background becomes as a means of protecting player character agency from the GM utilizing the warlock's patron as an RP tool against the player.
In both (1) and (2) the GM utilizes the warlock's patron in a manner that disrespects the player's sense of play. These effectively encroach on the player's creative agency.
* This gets into another topic that has been alluded to and implied but not yet discussed: Classes are imperfect archetypes. Often players view classes not as a set of prescriptive flavor text obligations to "play your character like this" but simply as a "line of best fit" for their character concept. I know people who would love playing clerics - as the mechanics fit their playstyle - but they hate the religious flavor text baggage. This is incidentally why I know that some players I have played with loved the unspeakable warlord. So I think that the practice of looking the other way when it comes to deities, oaths, patrons, and such stems from this problem. (Cue obligatory interjector: "That's not a problem; that's a feature!") I know from my own experience that there are players who like how the warlock comes equipped with a lot of player choice points (patron, pact, invocations, spells, etc.) and how it players but they likewise don't want the patron used against them. I'm okay with treating that "fey warlock" as a "fey sorcerer" or a "fey wizard" if that works better for that player.