He's 31 dude... not what a typical new signing would be. He still plays like a 25 year old but that's beside the point, it would still be seen as a gamble by most clubs. That's also not the only reason, I'm sure Atletico is definitely not keen to let him go now. He and Kun Aguero essentially carry that team
Plus we have a load of talent already, this is a similar argument against those who wanted us to sign Torres even after signing Villa, when we don't need more people up front.
Forlan is one of my favorite players but that doesn't necessarily mean that he needs to be at Barca. Getting him last summer instead of Ibra would have been ideal but it didn't work out that way, now it's too late imo.