You can find your answer here
" Making all legendaries obtainable/tradeable
[...] In PRO, legendaries are considered rare rewards that players can only obtain after completing long quest-lines and investing enough time and effort. We purposely will not make them readily obtainable like other games might - our goal is to keep legendaries unique and properly "legendary," so it doesn't make sense to compare PRO to other Pokemon games in that regard.
Additionally, legendaries will always be untradeable. This was the compromise that allows them to be in-game without melting the game's economy. We already had a well structured and thought out discussion even before starting to make PRO even (2 years ago) regarding legends and this plan wont change due to the MMO structure. "
Have read that and its just not making sense, and we are talking about catch-able legendaries here.
Making them trade-able wont hurt the game's economy, i can assure you that.
Yes its rewards as the staff mentioned "In PRO, legendaries are considered rare rewards that players can only obtain after completing long quest-lines and investing enough time and effort." but, its just not right to give rewards with RNG factor when you can only try it once!! not to mention everyone put same amount of time and effort to do the same quest. It's like LUCK are above EVERYTHING, you can't even beat the LUCK factor with EFFORTS and its very unhealthy for MMO environment. Can you name a famous MMO that put LUCK factor above EVERYTHING? when effort can't even beat the LUCK factor?
And as i mentioned before decent & epic legendaries give the owner a better edge and a wider option in team building and its not fair AT ALL.
It's different story if they gave legendaries with exact same IV to everyone.