Text/instant messages have evolved their own norms, as all language does. To many people, periods have a different meaning there. See e.g. https://www.npr.org/2020/09/05/909969004/before-texting-your...
My personal nitpick is people writing a stream of one-sentence messages without punctuation instead of a longer structured message - that definitely carries the connotation of unstructured thinking to me - but it doesn't have much to do with full stops per se.