Help me figure out what this girl is thinking! Why does it feel like her conversations skills start out good but progressively go to flat answers?

I met this girl at college and we have a snap streak of 240, but I didn't realize how much I liked her until recently. With summer starting we're both home and she's about 30 mi away. She always answers snaps and responds to everything even just pictures of our faces since the beginning of the streak. We probably send each other about 3-6 snaps a day EACH depending on the day.

I've been trying to initiate conversations more but I've noticed she will always thoroughly answer the question but never add on to the conversation. And after about 5-6 snaps its obvious she wants the conversation to be over where she'll use dead end answers.

In the beginning she will have full intriguing answers where it feels like I'm talking to a great friend but as time goes on she starts getting dryer. To the point that if I ask a question she'd only respond with an answer to that question. Thats fine but when it's a basic reaction or flat answer for 3 snaps in a row it's clear she is done. Why are the conversations when I start interesting with both parties obviously contributing to the conversation but over time die out on her end. Conversations would die way faster if I wasn't so eager to keep them going. If I were to go off on an anecdote and not ask a question she would just have a basic reaction like "thats so cute" or "lmao thats hilarious".

What makes me still cling to hope is the fact that she usually replies to everything very quickly sometimes within a minute. And obviously takes photos that make her look very good or at least avoid her "bad sides". Like bathroom photos, cute facial expressions, full face shots, her in a towel, or sometimes if she's at the beach just straight up cleavage shot (female IRL friends have seen her snaps and think just w the photos it's obvious she likes me).

In essence, why does this girl seem interested in me but when time comes to actually talk it starts off good but feels like she's intentionally leading it to a stop?
Help me figure out what this girl is thinking! Why does it feel like her conversations skills start out good but progressively go to flat answers?
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