You hit the nail on the head in the last paragraph. Some got bored but by far the biggest number of people I know that left the game fell into the category of Life. A lot of us were in the 25 year old to 35 year old range when UO came out and were hitting peak points in Careers, having kids, and those damn adult responsibilities taking a ever increasing amount of our time. Ran across a couple of old friend IRL that used to play who are in their mid and late 40s and the conversation turned to UO and the fun we used to have back in the day. Jim says "To bad UO isn't still around." Tom says "Yep miss that game." Mike (Tyrath) Says " I still play when I can through the summer and a lot over the winter." Jaws dropped they had just figured UO was gone. Since Wednesday both have retrieved their old accts, activated them, upgraded them and are sorting through their toons and playing again.Funny story when I bought UO it was UO:R and I fell in love instantly with the game... I knew my brother was a big game lover so at Thanksgiving that year I was going on about how I loved this game and he having actually played early pre-Tram UO looked at me with disgust in his face and tone and said "OU? That pile of **** WTF?! You couldn't pay me to play that ****! WTF you want to play that for?!?! That game sucks!" And we never really spoke of it again... he now plays WoW... which I give him a hard time about playing his Pokemon/Panda game...
And he won't ever return... even with Tram... even with all the changes. He won't even look at UO. Now my Sisters... I tried to get one of them to play even made a character and got her to log in... but she claims she's "too busy" to play a stupid game... and the other well... she and I are related somehow but she doesn't game. Must be a generational gap or something I don't know... she doesn't even own a computer... just her silly tablet.
Sad fact is UO has lost a number of players over the years and many of them... are like my brother... they would NEVER return... their experience with UO was so bad that nothing the DEVs could do would ever bring them back... UO fills them with disgust. Either due to their early experience in Pre-Tram... or experience with losing things from hackers, scammers, or glitches that cost them dearly and the experience scared them so deeply that they divorced themselves from the game so completely they won't ever return.
The ones who might return someday are the ones who just got bored and left... life got busy and they had to go... or they fell on hard times. But those scared and divorced will never return no matter what carrots you dangle or how many shinnies you try to bribe them with.
I wonder now how many players like them just plain don't know the game is still here after taking 10-15 years off to take care of business IRL.