In the last 2 years loads of stuff has been added. Perhaps it’s just not what you are looking for. Generally people make stuff that they want or like so it’s not always going to align with what someone else may want. SI themselves have also contributed a lot of stuff but it is a community store so revolves around contributions from the community. There are man contributing factors that limit what’s available.
If any of those instruments you shared have assets or code from someone else’s work you shouldn’t share them without permission. If they are 100% your own work then that’s fine. One of the issues with modding existing instruments is having a clear indication from the original author of their wishes right there in the instrument information so one knows ahead of time if the assets can be re-used or not. This has been discussed before but as yet nothing has been implemented.