*Nobody's running the types of things I want to play in, so I don't get to play in the types of things that I run for other people and I'm frustrated about that. (this sometimes morphs into the dreaded OMG this place is populated by people who don't take RP as seriously as I do, since they like different and less meaningful things, if one isn't careful.)
This can be so, so disheartening. It's happened to me many, many times. It's quite a lucky thing when you get to a place where two people want to run and play in the same type of stuff, so they can feed each other and keep each other sane.
*If I run something publicaly, it tends to get cluttered up fast with players I don't like. (who don't engage and probably are going to come to MSB and bitch about how boring all PrPs on this mush are within 5 minutes of finishing the 3 hour scene that I had to pester them to pose/do their action/ect the entire time or who would wait for 40 minutes to give everyone a 1 liner pose that didn't react to anyone else's pose)
In my opinion, this can be solved by staff offering support for a player's right to refuse service to anyone they feel like refusing service to.
Nobody owes anyone else their creative labor.
I'd tell any player they have the absolute right to tell someone not to show up at their scene. "You dialed it in last time and that sucked my energy away so I won't be adding you to this one," is valid and okay, and in my opinion staff needs to back that. So is asking someone to leave a scene. "This is the third time I've had to ask you to pose and you gave nothing to work with. That's disrespectful to the other participants and to me, and I'm going to ask you to leave." Policies should be supportive of the fact that someone who is asked to leave has no real choice but to do so, if the code doesn't allow you to just straight up remove them.
*I'm over here working my ass off, running a ton of stuff for people to help take stuff off staff's plate, but it looks like instead of inviting me or securing me a spot in stuff that other people or staff are running, they're just doing stuff with themselves/their usuals.
This one is harder; if what staff is running is mostly public they get who they get. I get baffled by players who say this but don't sign up for the public fun on offer, or put in +requests, or otherwise use the tools. For this I would think communicating clearly: "Hey can I get into this, hey can you save me a spot, hey can I follow up on this lead, hey do you have any mysteries coming up I can participate in, hey would you be available for some RP..." would have a favorable response. Sometimes staff just doesn't know how to include a player more directly, is staring at their sheet or their backstory and is at a loss for a hook or an angle. Sometimes staff isn't aware they're interested or care about that RP. They might just need to hear from the player in a non-accusatory way.
*The system rules/lore is confusing and I get anxiety just thinking about putting myself out there that way as a storyteller.
The solution here may be for staffers to offer themselves as "rules support". Player tells the story, staffer offers back-seat drive guidance till they feel more confidence. I've done this for players before and am more than willing to do it again...but I haven't always been good about communicating that fact. Note to self for current project!
*As a player participant I see people do no-shows, act like entitled assholes OOCly, try to run over/backtalk the ST, bitch about how they never get to do anything fun on a public channel while participating in this STed scene, argue with the ST over rolls/mock or not shut up OOCly about rolls, ect ect--fuck that, I don't want to risk having to deal with people like that.
Weirdly I've seen less of this over the years, not more. Most players I've run into and have run for have been kind, appreciative, helpful, and forgiving. Everyone's mileage surely varies there, though. I offer this not as a refutation but more to offer a sense of hope...many players are awesome!