[JorgeGT]

Time travel will be highly controlled by the authorities, probably that party was surrounded by future cops looking out for rogue amateurs.

[Bombthecat]

More like that you need tons of resources, skills and knowledge to do it. Nothing a private person could do.

[benibela]

But if the time machine itself travels through time, an unbounded number of people could use the same machine at the same time

[jotm]

I guess same way no one has used a nuke or even a dirty bomb yet, even though the latter would be technically feasible for even a small group.