Creating a human or animal from scratch is a very fundamentally different process than curing a disease. Teleportation has literally nothing at all to do with curing disease in even the remotest sense.
Why would the Institute have spent time trying to come up with a cure for ghouls? What reason would they have for wanting to do so? The Institute has finite resources and a finite number of people. They can't research everything at once.
To use another example, this is like saying "why are we wasting time studying particle physics instead of curing cancer?"
Answer - Because those things have very little to do with one another. Someone that studies particle physics likely doesn't have any ambition to study cancer. Similarly, the people designing and building synths wouldn't have had the resources to spare to try and cure the ghoul condition. And this is all rather beside the point, because you can't really 'unrot' something.
There's nothing fundamentally preventing us from doing so aside from technological limitations. Teleportation isn't impossible. We're just a very long way from having the technology to do it. Like a seriously long way. There's no reason that we can't create humans with machines. We ARE machines....we just happen to be biological machines. We still have a parts list though. We come with mostly standardized components. There's no reason that you couldn't build a human from scratch. Again, we're just a long way from having that kind of technology, and there are lots of ethical considerations and so on.
You can't unrot something. This isn't a matter of technological limitation, it's a matter of the fact that once something has rotted, it is no longer what it was prior to rotting.