Bo is playing beneath his talent level this season, and simply appears to be having a bad season. The constant whinging about Bo is getting old in a hurry. We don't know the Jays clubhouse dynamic, but by all accounts Bo is a fiercely driven/competitive guy. We really don't know how he would react to a demotion. He seems to be in the same mold as Marcus Semien where he busts his ass in order to condition himself to play every single day, and wants to play essentially every inning of every game. It may be in his best interest to back off a bit, but he's displayed a strong ability to remain healthy, and until this season was on an upward trajectory performance wise as well.
Cavan Biggio started the season with a -10 WRC+, and found himself out of a job. Despite Bo's struggles, he's still on pace for a 3 win season. Do you really think the club is going to be helped in any way by sending Bo down to AAA? Bo started the season slowly at the plate and in the field, but since May 1st he's been playing at over a 4 win pace when prorated to an entire season. For a player that's not been at his best that's still well above average.
It's really up for debate whether Semien was a better shortstop defender than Bo was last season. When you examine the metrics on a rate basis Bo was actually better by OAA than Semien was. Semien makes less errors at the position, but that's the only advantage he has over Bo. Bo has more range, a stronger arm, and has more ability to make tough plays than Semien. I wish I knew of a method for parsing defensive statistics over time, as I have a feeling that having the ability to examine Bo's OAA numbers of the course of this season would paint a very interesting picture. If I recall correctly he was in the range of -7 OAA at one point this season, and due to a very steady run of play over the last several months has managed to work his way up to exactly even at 0 OAA.