Plus its not that surprising TIM might go for controlling the Reapers I mean in the first game Cerberus was trying to control Rachni and Thorian Creepers as part of a slave army, and in Mass Effect 2 they tried making a VI god to control the Geth, and had in the past tried to create a super biotic, as well as TIM seeing the Collector base as a means to allow humanity to not only defeat the Reapers but any other races he sees as threats.
So it look obvious that he is after anything that gives humanity an edge over the other races so why wouldn't he try to go for the ultimate one and control the most advanced race in the universe. Especially since if he succeeds no one could oppose Cerberus or humanity.
The problem with that point Hart is that most of those attempts to control something WERE COMPLETE FAILURES
. Sovereign was able to control the Geth without anyone knowing and was able to launch an assault against the whole galaxy. Cerberus' attempt at controlling the Geth with a VI was not only a failure, it killed all but two people in a densely populated science station. The VI also would have caused more damage had it broken free. EDI herself managed to no longer follow Cerberus' commands, and even the collector base didn't amount to jack in the end. And depending on your play, he wasn't able to control Shepard either.
So why should TIM, who's writers declare that his intelligence is his weapon, think that he'll have more luck controlling the Reapers when he couldn't even control the GETH? Again, the same synthetics that the Reapers themselves were able to control and manipulate with ease. His motivations are like a fourth grader who keeps failing his math classes and decides he's going to tackle integral calculus instead.
Hell, even Joker was -- ahem -- joking about that in the Citadel DLC. Years ago, before anyone knew anything about them, Cerberus tried to create a superbiotic by torturing a small but talented child; that child got loose and killed all their guys. A few years later, Cerberus tried to make an army of Thorian Creepers; they got loose and killed all their guys. Then they tried to create an army of Rachni; they got loose and killed all their guys. They tried to experiment on Thresher Maws, which got loose and killed all their guys. A few years later they experimented on a Geth-controlling VI, which got loose and killed all their guys. Around that same time they resurrected Shepard, who became disillusioned with their methods, got loose, and killed all their guys. Shepard was aided by EDI, a powerful AI construct who later got loose and killed all their guys. On Omega, they were experimenting with adjutants, who also got loose and killed a lot (but not all) of their guys.
The Illusive Man's whole resume has been a litany of futile attempts to control things that he barely understands on the assumption that they will somehow, someway, become more of an asset than a liability. That's the entire idea behind Cerberus: they cruise around the universe playing with every kind of fire they can find on the assumption that sooner or later they'll figure out how to control it properly. Their attempts to control the reapers would have been equally futile; even if they had any early success, it would only be a matter of time before the Reapers got loose and killed all their guys.