ok- so if I understand those terms, roughly(?):

support --> contact system for humans to reach other humans with bugs or questions

indemnity --> a legal statement by the vendor that the client is not responsible for long term liability for patents or legal challenges

assurance --> a legal statement that the vendor will take responsibility if the product is not what it appears to be, or is missing parts that are required to fit a purpose

establish a legal framework --> define the copyrights and governing law for rights, responsibilities and disputes between the vendor, their suppliers, the customer and their agents

Spot on. The kind of features that accountable execs care a lot about. The engineer’s conception of companies like IBM and SAP and Oracle is that they sell terrible clunky software, but a substantial part of the value comes in the CYA that the above brings. The users are rarely the real customer.

For a concrete example, have a look at SQLite. SQLite is Public Domain, but it's used virtually everywhere, from phones to airplanes (https://www.sqlite.org/famous.html).

Not all companies are going to trust that something is actually public domain. So, you can get a "Warranty of Title" for SQLite. See https://sqlite.org/copyright.html

And those companies might not be satisfied with "community support". So, you can get paid support for SQLite. See https://sqlite.org/prosupport.html