If open-sourcing the algo allows bots to game the system then it has value to the bot wranglers; if the feed becomes full of garbage that gradually destroys Twitter's value.

Any worth that "the algorithm" has is not in it's implementation (probably pretty standard ML prediction systems), but in the training data and weights. In isolation from the data and the rest of the code it is probably pretty useless as anything other than an example of real world ML use.