1) Bosh wanted a dynamic PG who could penetrate and create opportunities for him, since that was the way the league was going back then, so BC traded PF depth (Charlie V.) for a young PG (Ford)
2) Bosh wanted to shift to PF because he was sick of getting hammered while playing C and wanted to be able to focus on offense instead of defense (hmmm who does that sound like now), so BC traded PG depth (Ford) for a proven C (O'Neal)
3) Bosh & O'Neal didn't pan out, Bargnani was looking like a decent talent (and looked to be developing some good chemistry with Bosh) and the overwhelming consensus was that the team was lacking a stud wing, so BC traded C depth (O'Neal) for a proven SF (Marion)
4) Marion seemed destined to leave the team for nothing and the team drafted a highly touted wing (DeRozan), so BC replaced one proven wing (Marion) with another proven wing who had a glowing reputation as both a distributor and 3-pt shooter (Turkoglu), to help spread the floor and give Bosh more room to operate
These moves were all home-run style moves that didn't pan out, but BC deserves credit for making them AND for correcting them when they didn't work out. He tried his best to build a solid team around a player perceived to be a franchise player in Bosh... the biggest problem was that Bosh never was a true franchise player... he was a good player on a terrible team. For 7 years, nobody faulted BC for building around Bosh, so don't start knocking him using hindsight!