It's just motivated reasoning. There no reason whatsoever to believe that guy who stole it actually needed or valued it more than you.

It was free for him, he didn't work for it, it doesn't hold the baked in value of what it cost him to get it and statistically speaking criminality has a strong negative correlation with conscientiousness, so he likely doesn't even value the things he did have to pay for as highly as the average Joe. There's a good chance he just rode it as a single use conveyance and dumped it in a ditch somewhere so as to not get caught, there's even a small chance he used it to aid in committing another, even more harmful crime, decreasing total happiness even more.

There is a chance he sold it, but even then the guy who ended up with it traded money for a bike, he's not ecstatic about that transaction, he's marginally more happy with it than the goods he traded for it, that's the essential pattern of commerce. And someone who would buy shady bikes off a stranger (or a guy they know, and know steals bikes) is also likely low in conscientiousness and tends to feel no great care over anything they own. But maybe against all the odds it ended up with a good-natured but desperate guy, down on his luck and just looking for a way to get to work because he couldn't afford to fix his car. That'd be nice, right?

The only time it's actually more likely than not that the theft somehow ended up with more people being happy is in the extreme circumstance where the bike you owned meant almost nothing to you, either because you're filthy rich or you hated it for some other reason. But you were bummed initially, so it doesn't sound like that's the case for you.

People want to feel better about the events that lead to their bike being stolen and being unable to recover it and restore the rightful order of things. Some people get mad and bitch and moan for a while. Some people are just good at letting it go. And sometimes people who are concerned with concepts like "total net happiness" chose to believe in the fraction of a fraction of a fractional possibility that somehow it ended up helping someone who deserved it more, rather than the most likely outcome that it was just a selfish cunt who benefited at your expense. To me that's no more rational than drinking the spicy kool-aid on the fraction of a fraction of fraction of a chance that Mr. Jones was right and it will actually take you to Nirvana.

It's also kind of understandable though, in a pitiable kind of way, people who do have a lot of empathy are bombarded with pleasant sounding lies like "revenge is always bad", "it's always better to just walk away" and "the only thing you need to do is tell a teacher and everything will be fair in the end" from early childhood, and some really do internalize them out of pure goodwill for everyone else. Accepting that they did everything they were supposed to and were just complicit in making the world worse is a bitter pill to swallow after all that time.

Then there's major the flaw in "total net happiness" itself. It's a broken system that assumes everyone's happiness is equally valuable and fails to account for which actions actually deserve to result in happiness. Come to think of it, you can basically just sum it up as emotional communism instead of financial communism. For example, one way to maximize "total net happiness" in that situation is hunting down the guy who stole your bike, kicking his ass, taking your bike back and smashing both his kneecaps, you just have to make sure to really fuckin enjoy the process, so much so that it outweighs his suffering. Seems pretty messed up, right?

You can take it even more extreme if I have to. A guy works extra shifts for a month to save up and buy his son his first ever game console. But the kid is at school half the time and can only play in the evenings. Across town three child rapists share a cell and would really enjoy that console since they're in locked in their cell 23/7 to prevent them getting shanked in gen pop. So the father decides it's best to give it to them instead. It's not actually a very happy world, it's just fucked up. It's also a very simple world, you don't have to make value judgements about what is good and bad, just who has more and who has less, the more confused and insecure you feel, the more appealing the simplicity is.

There's been lots of game theory around how altruism even came to exist as a naturally selected heritable trait in humans, and the general conclusion is altruism is abused and goes extinct in every environment except one where altruists can recognize each other and only extend their selflessness to each other instead of the entire population. Likewise an honor system only lasts for as long as there is someone willing to enforce transgressions against it, and enforcing the rules is actually kind of unpleasant for empathetic, honorable people. So the fairest system is if everyone accepts a small portion of that responsibility themselves to punish transgressions, instead of absolving themselves of making the instinctually unpleasant but necessary hard choices.

So bike cuck is just an exemplar of that kind of abdication of personal responsibility for making the world better, all wrapped up in an air of morally superior martyrdom, which is gonna extra piss off the people who refuse to live in that happy delusion and want to actually save good people from a life of crushing oppression by selfish assholes.