We don't know enough of the situation to make a comment on why he was sold for that price. Everyone is acting like we needed to start a bidding war for him when literally NO CLUB was showing any interest at all in him for two years (I don't take the Man U/Arsenal stories seriously, 99% of that was pure BS). I personally think he's worth closer to €50m, but again, who am I to determine his worth? None of us are privy to the inner workings of football transfers and I think it's best we leave it to those in charge of the club to do what they have to do.
IMO though, he obviously wanted to leave, Bayern had leverage, could obviously offer him a lot more money on a longer contract, so we cut a deal with them as best as we can. It was either that or lose Vidal a year later for €20m, or free a year after. It sucks, but we have lost better players than Vidal in the past. Let's not carry on like a small club would in losing a player. As always Juventus >>>> any player.
It's hard to make assumptions, but we have facts to work with.
1) Vidal is widely regarded as one of the best midfielders of the world, the best box-to-box there is;
2) His contract ends in 2 years;
3) Bayern approached him, he accepted the offer and informed Marotta, who decided to sell.
4) The price of the sell is lower than his value of the current market, specially considering the pound-to-euro value.
5) He was sold before Marotta had an adequate replacement at the AM position.
This is all factual. We don't know if Marotta shopped him out or not; if he didn't receive other offers. But the price indicates that Marotta didn't shop him around, it's an assumption, like many we do everyday when following football.
Also, I don't see this as Marotta didn't have other options. He decided to proceed this way, selling him quickly to go after an AM. But he could have done differently, as far as we know. So considering he had other options, I simply don't agree with how he proceeded, even though the final result can still be good and we'll only know it during the season.