When I built my enterprises, I never stopped building and I didn't bother to transfer money to pay off the debt. I already knew my corporations would be profitable, so paying back the loans would be a matter of time.
I racked up 35T in debt while building 750 corps. Eventually, it was all payed away and I now transfer 5T out of the enterprise every week.
I have not bothered to keep my myself up to date, but I believe the rules are now different from when I finished building my last enterprise. The initial capital of all corporations was 100B, I could build corporations even when my enterprise was in debt and enterprises weren't forced to inject capital into when corporations we're at loss; so young, unupgraded corporations could keep their debt, instead of having it transfered to the enterprise in practice.
For that last aspect I mentioned it may be why you are still making a loss: your corps are not fully upgraded. It may also be you are building the wrong kind of corporations, but since new players tend to copy what older players build, I doubt it.