I slept too much today; I didn't get up until 5PM.

"Sleep too much" and "sleep until" are both valid constructions on their own, but combining them doesn't really work. I think you might be able to get away with it if you placed a comma before "until," but I would prefer something like this.

Maybe, it's because I played soccer with my friends until 5AM.

Verbally, there can be a pause after "maybe" if you're making a suggestion, like you are here, but in writing, there is generally no comma.

I love dogs too, but I'm absolutely a cat person.

To be honest, I don't know much of areally know the reason why myself, but I love cats.

I've never had a cat due to the rules of my house even though I love cats so much, due to the rules in my house.

Or, if applicable, you could write something like:
- my apartment rules
- because my apartment/lease doesn't allow them
But these are mostly situations that come up if you're renting or if you live somewhere that might restrict pet ownership, like certain high-rise buildings.

I slept too much today; until 5PM.

Maybe, it's because I played soccer with my friends until 5AM.

For that reason,That's why I don't have a particular incident today to talk about today , so I'll talk about cats.

"For that reason" is correct, but "that's why" sounds more natural in speech.

I love dogs too, but I'm absolutely a cat person.

To be honest, I don't know much of a reason myselfmyself don't really know why, but I love catsthem.

I've never had a cat due to the rules ofin my house, even though I love cats so much.