One obvious is trust. Secure Elements are validated against Common Criteras, often at very high level (6+). Yet, there have been problems. An example is bad RSA

One obvious is trust. Secure Elements are validated against Common Criteras, often at very high level (6+). Yet, there have been problems. An example is bad RSA implementations. Developing for SEs normally require signing boatloads of NDAs. This makes it hard do talk about weaknesses, things that simply could easily be improved (in support libraries for example). By having open designs, open source more people can review and decide for themselves if they are ready to trust the SE. And hopefully more bugs can be found, issues can be fixed and things can be improved faster. This will benefit the users and the societies as a whole.