Esports tournaments actually do get cancelled due to real-life events, especially when it comes to major tournaments which are common with games like DOTA 2 and CS:GO. There are also exclusively online tournaments, but they're usually reserved for smaller events and lower-tier matchups and it's generally ideal that higher-tier teams play in person.

On the CS:GO side of things, the anticheat programs employed in third party services outside of Valve's own system are actually extremely sophisticated and manage to filter out almost all cheaters, but there are indeed incidents where external devices are used to cheat and such.