To be fair, in the case of something like a Linux ISO, you are only a tiny fraction of the target or you may not even need to be the target at all to become collateral damage. You only need to be worth $1 to the attacker if there's 99,999 other people downloading it too, or if there's one other guy who is worth $99,999 and you don't need to be worth anything if the guy/organization they're targeting is worth $10 million. Obviously there are other challenges that would be involved in attacking the torrent swarm like the fact that you're not likely to have a sole seeder with corrupted checksums, and a naive implementation will almost certainly end up with a corrupted file instead of a working attack, but to someone with the resources and motivation to plan something like this it could get dangerous pretty quickly.

Supply chain attacks are increasingly becoming a serious risk, and we do need to start looking at upgrading security on things like the checksums we're using to harden them against attackers, who are realizing that this can be a very effective and relatively cheap way to widely distribute malware.