There are three channels for import of Schedule K-1 data:
When online tax applications began 20 years ago, they did not include a Tax Exchange Format (TXF) or other file import feature. Instead, online tax applications began importing data using the Open Financial Exchange (OFX) API technology.
The problem is this: OFX-formatted data is only delivered via API, with few exceptions. Setting up direct system-to-system API connections between each of a dozen or more tax software applications and thousands of tax data providers is impractical for the industry.
Adding file import will allow any tax data provider to publish electronically-importable files.
See this article by the Financial Data Exchange standard-setting organization.