Getting a computer to figure out where English sentences begin and end hasn’t been perfectly solved. There are libraries that do it, but they all seem focused on getting incrementally closer to how humans handle rare, ambiguous, or grammatically incorrect cases (and publishing academic papers along the way).
As a small part of a fun side project that’s just getting started, I needed sentence breaking specifically for well-edited text. For example, if someone forgot to capitalize the start of their sentence, I’d rather just move on than try to compensate with something that could misfire on valid sentences but makes a great research paper.
Besides, the whole project is for fun, and writing this part sounded fun.