#2 His age counts against him

The midfield is the engine house of any football team, as players in this position are usually charged with doing the most work on the field by linking defence with attack and generally covering the most distance on the field.
Hence, for this reason, mobile, agile and young players are generally preferred in positions of midfield balanced with a touch of experience, more so at Barcelona where their possession-based style of playing requires great emphasis placed on their midfield.
The departures of club legend Xavi and gradual decline of Iniesta put the Barcelona midfield in the spotlight for the wrong reasons, and the club gradually lost its creativity, with the effect being that Barca's chief goal threat in Lionel Messi had to increasingly drop deep in a bid to influence proceedings.
The club faces something of a midfield crisis, as their main midfielders Ivan Rakitic and Sergio Busquets (other than Arthur who is just establishing himself) are all on the wrong side of thirty.
It, therefore, made no sense adding a 31-year-old Arturo Vidal who had at most just a few years of elite football left in him, and to make matters worse, he was offered a three-year contract.