Is this referring to Tesla's "patent pledge" or some other offer?

Because the patent pledge was a bit of a joke. It amounted to "You can use Tesla's patents, as long as you agree not to assert any patent or other IP against any company for making EVs or related equipment."

So you don't just have to let Tesla use your patents in exchange for you using theirs, you have to give them away to every competitor, whether or not those competitors are sharing their own patents. It's not surprising that no one has taken them up on this.