I think before, it was easier to spot. Before, the effort spent would often show in the volume or consistency of the writing. Now, one can create a big, wordy and convincing-sounding document (without any grammatical errors!) in mere seconds. It also provides for some convenient plausible deniability: you can always claim the LLM only helped you here and there with the wording.

So now, even figuring out that it was a careless or lazy job takes a lot more time, which drastically skews the economics in favor of the careless person.