Because they are cheap and over-powered.
If you count sudowoodo as a legendary then yes
No. no superpower Pokemon (rayquaza, mewtwo, regigas, groudon, kyogre, etc.) are allowed in the battle frontier.
You can see all kind of Pokemon, except legendary Pokemon.
No its not, legendary Pokemon like that are not allowed in.
You can access the Battle Frontier and you can catch some legendary pokemon.
No, Pokemon Sapphire Version does not have a Battle Frontier. However, Pokemon Emerald and Pokemon Platinum do have the Battle Frontier.
You can find legendary Pokemon in Pokemon battle quest in the pokeshop.
I snuck Latios and Manphy in but dont know how
Pokemon Ruby and Pokemon Sapphire do not have the Battle Frontier, instead they only have the Battle Tower. It was not until Emerald version that the Battle Frontier was added to the game.
If you see a Pokemon in the battle frontier you have not yet seen, it will not record it. The only way you can add that Pokemon to your pokedex is if you see it outside of battle frontier.
There is no Battle Frontier in Pokemon Diamond and Pearl. Only the Battle Tower.
no you can not get exp in the battle frontier in Pokemon plat