Betting on both sides is pretty stupid unless the odds change over time or are different on different sites so you can guarantee yourself a victory.
Or if you do something like Team A -8, Team B +10 so there is a middle where you can win both bets possibly.
Talked about this in past posts.
And yes, nobody said that you can't bet in 2 different sites, usually odds are different in both of them, like i said this way needs a lot of math. also it is good for people that don't want to know more about teams, so they can just count odds and that's it.
This is because it is safer to risk your money if you know how your predicted team will win than based on random luck alone.
Yes, this is also a good reason.even if you can't be 100% sure that team you bet on will win, it is still much better to bet on team, then on RNG.