Testing could be a reason.
To be clearer, I’m not sure these keys were generated, but being able to use weak keys is something you may want to do for testing.
What testing would require it? I've done plenty of testing setting up internal CAs & HSMs, and none of it required weak keys. Generating a key with the same parameters as a real key is trivially easy, and has the benefit of testing your key generation at the same time!