She has short attention span and forgot - don't blame her, text more girls, keep creating content. chances are, she'll notice later and chase you
You've sent more words/sentences than she has (investment dynamics. always count how many letters you're sending, always send less than her)
You've hearted a message she sent ❤️ (big mistake. these little social media hearts ❤️ are powerful. there's a reason why they're everywhere - they're psychological currency. when you heart her message, she gets all the validation she was after. as a man, we need sexual intercourse to get full validation from the opposite sex - girls just need this little double tap. when you double tap, you break all sexual/validation tension, there's no more novelty, therefore no reason for her to stay in the interaction.
Which one do you run most into? Would you add anything to this list?