Because the sports governing agencies have such a great record of enforcement against such regimes, e.g fifa, formula1, atp etc.

This won’t do anything.

It actually will… having to compete under an anonymous flag will still marr the nationalist propaganda these events are used for back home. It might not affect Russia that much (since Russia doesn’t really care what the west thinks about it) - but it will probably be a whole lot worse for Israel.

A sports boycot in itself is not a very big thing… but in the end every little bit helps, no?