Not all environments are as dusty as the next.
There are a host of factors that play into this, both environmental and human caused.
Depending on the region in which you live, you could have lots of dust around your house, or even airborne sand if you live in the desert. Mold spores in the air and on the ground outdoors vary to essentially the same degree. Before even looking at human factors, you already have a lot of variation in what affects one area versus another. What makes all of this worse is when you combine these natural environmental irritants with construction work. You could have ceramic dust in the air if there is concrete being cut nearby. Likewise, if trees are being cut or wood houses being built, you could have an equal amount of saw dust with whatever natural dust is rolling around. You can make this worst within the confines of your house by simply doing laundry more than the next person. Since my region is full of irritants, I use an air purifier to clean out most of my indoor air before it gets a chance to enter my HVAC system and go into the ductwork throughout the house. I will often find lots of particulate building up on the air purifier filters as quickly as three months after replacing them. It’s worth the hassle and the cost, because my asthma issues have been knocked back considerably. I can’t imagine living without an air purifier now that I’m so used to them. As long as I can afford to buy and replace the filters, I will use the machines until the end of time.