From 2008-13, there were few players in baseball more valuable than Evan Longoria. At this point of his career, he was on a hall of fame trajectory. He had a career 135 wRC+ to date, he was an elite defender, as well as an above average baserunner. Additionally, he was a perennial all-star candidate, and one of the faces of baseball.
From 2014-2017, however, his bat became closer to league average (108 wRC+), and defensive metrics painted an inconsistent picture from year to year (though still solid as a whole). After the ‘17 season, the Rays looked to go in a different direction, and saw the Giants as the perfect trade partner.