Because it’s better to not submit a cover letter than to submit something filled with generic AI generated garbage that doesn’t represent the real you.
You might get disqualified by some automatic process that filters on length. Nobody will most likely read those couple of sentences anyway. And ironically, if they do, they might think you're lazy for writing only 2 and would rather go with the guy that has a longer cover not AI-generated.
That is actually AI generated, because people thinking they can easily differentiate between them probably also think they are immune to publicity.
It's not unheard of to be applying to 50+ companies in the hopes of hearing back from 5. It's not a couple sentences - if you wrote three sentences per letter, thats 150 sentences.