I've been lucky. Since 2014 all of my 5e campaigns were played to completion.
My one campaign that went down in flames was my attempt to run a Mage: the Ascension campaign. A player in my group brought it up a number of times, suggesting that I would be a good GM for that game and he got me interested in the system. All of the players in my regular 5e group were up for a second campaign and alternating between MtA and D&D 5e.
I found the rules confusing but made a strong effort to learn them, buying various game aids in addition to the core books. I also created a custom MtA character sheet in Role (a gaming focused teleconferencing platform with light VTT features).
I think I would love being a player in a MtA game, but I hated running it. The rules just didn't come naturally for me. Added to that, I was very busy at work and trying to run two ongoing campaigns in two different systems was too much. I found prepping for MtA to be far more work. Rules aside, there were few published adventures and I wasn't that impressed with the ones I found. I plotted out a what I thought was a good overarching story, based mostly in Manhattan, with a good number of plots, stories, special locations, and NPCs. But, in the end, I found it to be too much work, I wasn't comfortable enough with the system to run a low-prep game, and burned out after a couple of sessions.
I find that I have to come to game on my own terms and grow a desire to run it on my own. Also, with my heavy work load, I don't want to spend all my down time on prepping games. I think my 5e campaigns are successful because I'm very comfortable with the rules and, while a put a LOT of time in prepping a new campaign up front, once it gets going, I find I have to do very little session prep. My comfort with the system, along with a huge number of game aids, also lets me improvise acceptably well.
The downside is that I mostly play D&D, though I do try to throw in the occasional one shot in a different system now and then.