[bastijn]

In academia you don't care about the quality of your code, in professional you do care but don't get the time to fix it ;).

On a more serious note. In addition to what is already mentioned by others on quality, performance and so on I'd like to add that in professional career you most likely work with a (larger) team. Which means you will run into code conflicts where code is reused for different purposes and you cannot simply change it. In addition you have to think about readability and documentation as your colleagues have to be able to understand the code without losing too much time or needing you.

You will also always have to work with legacy code. Most likely code you want to change but can't considering the timelines.

You will have to sync your design with many others. You might have to convince them or discuss issues with conflicting requirements or deadlines. There will be times you can't finish your entire design and have to think of a staged introduction or even harder, change it so it can work with only 50% of the design.

Also, your code has to run for many years. You can't simply take an expirimental third party package maintained by a single person. Too risky. You have to think about hardware expiring or no longer being supported (especially with gpus).

You gave to think about licenses. Academia is usually free. With professional you have to take a close look.