Hah, I am one of those who'll write you the longest bloody novel that ever existed as one reply in a roleplay to make you read it all!
Nah!
I write long posts
(2-5 word pages average, often longer, longest reply I have ever written was 28 word pages long in one post) because I am a sucker for detail, for flashed out characters, for elaborate, deep introspection, for painting a picture of the scenes outside and inside of the characters, their thoughts, their presents, their pasts, their philosophies, their dynamics with their surroundings, because I enjoy to create and to shape vivid and lively worlds, universes and stories with different types of characters in them.
The goal of my writing - no matter if it's a novels or a roleplay - is to accompany and follow my characters through their journeys and adventures that unfold and create on my mind like a movie and to get this across, to make it come to life and be able to indulge in their worlds and to invite the person who reads my work to to enter and lose themselves in those very worlds too while reading it and this is what I am trying to achieve. When it comes to roleplaying it is important to convey this as the roleplay partner is supposed to be able to experience the story and the universe created while at the same time it requires them to manage to be able to do the same thing with their writing and their characters for it to be interesting and worthwhile for both parties.
I also like to take on challenges, to try out new perceptions, different characters and worlds all the time. I like to grow and improve as a writer while I am actively writing. I am all for broadening my horizon and my repertoire.
This, to me, is what I consider to be fun about roleplaying and writing and what makes it such a great hobby and while one doesn't have to match my posts in length 100% and I understand that different scenes require different length in content, one has to give me detail, introspection, development, depth and quality, something that makes me able to get to develop an interest in the characters and the roleplay, to have substance to work with, that moves things forward and contributes as much as I do. I need something that motivates me to respond with something good to what I get!
And all of that's simply not possible with plain and short posts at all!
I can't work with short posts, they don't manage to get me hooked, they bore the living shit out of me and I will lose interest.
When I get those plain, shallow and short posts and haven't dropped it immediately, due to whatever reason, maybe because I see potential in the story, the characters or think there might be room for improvement and it could get better, I have the problem that I usually massively struggle to reply to those roleplays, I will often be unmotivated to respond and I'll automatically end up prioritising every other detailed, deep, lively roleplay with substance that is thought through, fun to read and manages to capture me over the one with short posts even though it would – theoretically – take me a lot less time to type up something equal in response to the short, shallow, plain one that doesn't contain much detail and information as a novella style one does.