It is hard to answer from what is in your question, but scenes you feel are too short are (in my experience) under-imagined, or under-conflicted, or you are engaging in too much 'telling' about how people feel or think, without enough 'showing' through action.
An under-conflicted scene is when something may happen, like a decision made or information imparted, but it is dialogue without very little opposition. No argument, no confusion, no "I've got a better idea", no "I can't do that, and I'm not doing that". Or it is action with very little obstacle: There is nothing in the way, no equipment failure, nobody gets tired or sick, nobody gets attacked.
"I have an idea," Mark said. "Let's walk three thousand miles to Los Angeles."
"If you say so."
Mark and Angela left Brooklyn, and arrived in the middle of Los Angeles six months later.
You have a physical setting to describe. People have thoughts and memories during conversations. There are pauses while they do that, if you aren't describing those thoughts and memories, it is a good time to flesh out the scenes. Pick a published best seller you like and see how that author does it, but set your vision to see what the author writes that is NOT dialogue. I have seen an author put a whole page of material (250 words) in the middle of a conversation, between one character asking a question, and another answering it. (In that case it was a relevant memory from the MC's past.)
The characters have feelings, both physical and emotional. Sights and sounds trigger memories: If I walk one block down my street, I can pick from fifty memories, if I tried I could make it a hundred memories. The same should be true of my MC, if he walks down his block, there must be something or somebody he can remember, depending on his mood and his problem, that might be relevant and influence his actions. Be it funny, or brave, or self-sacrifice, or a sadness he wants to avoid, or a success that inspires him.
The same is true for non-dialogue scenes.
I suspect you like the fight scenes because they have natural conflict and you don't have to struggle to find it. Write you other scenes with conflict, too. For my own writing, times when things go well for my MC are a few paragraphs at most; 90% of my writing is my MC beleaguered by one problem after another with larger problems preying upon them.
I won't go far into 'show don't tell', it is well discussed elsewhere, other than to say this: consider the ramifications or consequences of your descriptions. It is one thing to say "Mark was sad" or "Mark was handsome", but those conjure very weak images in the mind. If they are true, then there should be consequences that accompany those states, try to think of some concrete effect that Mark being handsome would cause. Or Mark being sad would cause. Even if that is in the MC, male or female: They can imagine handsome Mark in high school; for example.
If you can't think of any concrete consequence, then his appearance means nothing. Nobody, including the MC, treats him any differently. It doesn't make him charming, he hasn't used his good looks to become practiced at manipulating women or rack up a bevy of conquests, it makes no difference to the MC or how they treat Mark, so why waste words describing Mark this way? That should be your thought process, either find a consequence in Mark's personality or skills that is a result of him being "handsome", or ditch the description. The same goes for "sad". If Mark doesn't act sad, disengaged and lethargic, separating from social interaction, distracted by his internal contemplations and dismissive of other people's problems or difficulties, and his sadness does not have any impact on the MC and presents no obstacles to the MC: Why make Mark sad? Describe the consequences of sadness and the obstacle that Mark's uncooperative emotional state presents for the MC.
This may or may not be your writing style. Not all short scenes are bad, and a short scene can be more powerful for being short. Typically, however, short scenes are weak and would be strengthened by making them longer, like adding supporting cross members to a tower. Imagining the scene and the internal states of characters more fully, adding more conflicts, and showing instead of telling are ways to lengthen the scene in a meaningful way: It isn't fluff, it is more for the reader to become better immersed in the scene and characters.