Half of the fun for the true hobbyist is bringing a dead game back to life. Opening the manual and flipping through the pages looking for fuse values, part names and numbers, switch matrix, schematics, etc is so much fun. Reading through different forums and websites for advice and tech help is fun too. Then once you diagnose the issue(s), you get out the soldering iron out, novus products, wax, and all your misc bins of parts. Next you strip down the playfield, clean up everything, fix the mechanical and electrical issues, and put it all back together.
After it's all back working again and you have a shiny new machine that you can play, you don't actually play it because you're too tired and you just want to look at it while you have an icy cold beer. Which is just enough time to rest and once the beer is finished you play it until 3am (while continuing to drink icy cold beer). Oh god, you have to go to work in 5 hours! Screw it, the new game is too much fun.
Of course there are also people who buy NIB who don't have to do a huge job getting their game to work, which is totally fine and I have nothing against that. But personally for me, I get a lot of enjoyment out of this hobby when I can breathe new life into an old and dead game, and make it really shine.