I have been playing and DMing for over 25 years, and my personal record for campaign completion is ... not great. Like, at all. In those 25 years, I have been running games near constantly, usually weekly or bimonthly, though a few periods saw more or less. During that time, I had one straight campaign in AD&D 2E that went to completion (a homebrew personal campaign that was itself a mashup of Dragonlance and a few other elements), from 1st level to about 9th level. Between that my group would play a lot of one-off adventure modules, run by myself or other players, and the characters from those were persistent - though the setting wasn't!
Eventually that "between" campaign morphed into Greyhawk and I pushed it through to complete Return to the Tomb of Horrors. They then progressed into the Bloodstone series since they were all about 15th level, and the completion of those adventures I consider the end to that "campaign." When 3E rolled around I bought a lot of d20 material - like A LOT. Too much to run in all honesty. During this early 2000s period we played a lot of adventures but rarely was the term campaign considered. Eventually I ran several of the D&D "campaign" adventures, from Sunless Citadel up through to Heart of Nightfang Spire - but we didn't finish it.
Towards the end of the 3E era I ran the Age of Worms campaign adventures pretty much from start to finish, probably the longest single string of adventures in a storyline I've every ran. They finished, we dabbled in other game systems for awhile, and then 5E rolled out. My own player group wobbled a bit here and there so I focused mainly on AL stuff, at conventions and then at my local game store (The Source in Minnesota FTW!). I ran Dragon Heist to completion there that transitioned to Dungeon of the Mad Mage for a bit.
About 3 years ago I started up a campaign with my personal group with the intention of running Storm King's Thunder. I started with Legacy of the Crystal Shard and we had a blast, and then it moved into SKT heavily - and then bam, COVID hit and derailed the whole thing just as the party reached Maelstrom. I invested heavily in miniatures so I was loathe to move to online play for this campaign, but I did start up a new online game running a homebrew campaign focused on the planes I hope to polish up and release on the DMsGuild.
We picked up SKT recently and have only one session left (I relented and went online with it) and the planar campaign is at the one session left as well. Assuming both can get pushed past the finish line, my completion rate over 25 years is like ... 5 campaigns? 6 maybe? Doesn't mean I haven't had fun with it, and I'm looking forward to doing even more in the future!