I am curious how he turned out that way. You don't seem like you were raised by wolves, by he seems to have been. Did your mother scurry after him with a trash can and cleaning rag?
I can only speak for my brothers, but as I have 5 of them, it's a decent sized sample.
They all grew up doing chores around the house. They all knew, after they were about 10, how to wash dishes, scrub a floor, vacuum, do laundry, clean their rooms, set a table. My mother did not pick up after us, but made us pick up after ourselves. We knew not to take food outside the kitchen or dining room. We knew that wood furniture needed to be protected from possibly wet glasses, while the Formica kitchen table did not. We knew the difference between the daily Corelle dishes and the fine china that came out on holidays.
Without exception, my brothers moved out of the parental house and became slobs. Dirty dishes left in the sink until there were no more clean dishes. Dirty laundry left until there were no more clean clothes. Didn't own vacuums or dust rags or even many cleaners. The bedroom of one of my brothers was carpeted in clothing. He claimed there was a dirty pile and a clean pile, but I couldn't see any line of demarcation. Food and drink were spilled on sofas and chairs and they simply didn't care. Bathrooms--I tried not to have to use the bathroom at their apartments, they were so gross.
Decor was strictly functional. The bicycle parts were neatly lined up in the hallway. The guitars were carefully put away after each use. The furniture was from the thrift store, so it didn't matter if it was broken, or scratched or got spilled on. Why put clothes away if you are just going to take them out again?
I shared an apartment with one brother for three years and he thought I was nuts because I wanted things to be a little color-coordinated in the kitchen. (Thirty years later, I am still teased about wanting only certain colors for that kitchen.)
Sometimes they'd clean up their acts a little if they had roommates. But it wasn't until either a) they got serious about a woman or b) bought their own place that they started to clean up and take care of how things looked and wanted to take care of their belongings.
I do not wish to stereotype all men. I know several who are clean and neat and tidy and who live alone. But I do think that there is a subset of men who really don't care what their environments look like when there is no one else to see them. Not being of the same mindset, I have no idea what fuels this, but I've seen it in many more men than just my brothers.
And I can see, if they are used to living that way, how they would tend to treat their siblings' homes in the same way.