"or else" now has its own separate dictionary entry because people use the two word combo as a conjunction instead of just plain "or" or "else":

https://www.merriam-webster.com/dictionary/or%20else

> [He said to do this, or I'll regret it.]

> [He said to do this, else I'll regret it.]

I imagine people couldn't decide on which conjunction to use since they both work, used both incorrectly, stopped using plain "else", then started thinking they needed to prefix "or" before "else". Dictionaries then adjusted, removing the conjunction entry of "else" and adding "or else" as a conjunctive phrase.