I find the matts are worse when they are puppies. the puppy fluff seems to clog up near the skin, rather than down the hair shaft, & need to be brushed out every day. It almost seems to get worse as their coat is changing, then sorts itself out when the adult slky coat comes in & doesn't tangled nearly so much. except for round the elbows & behind the ears, & a bit more on the side they sleep on.
I do think clothes make it worse. No matter how tangle free mine are before I put a jacket on, it can resemble a bird's nest when it comes off
Harnesses do it to mine as well, though I know they're better for throats, no wonder the show Yorkies still wear show leads like my bigger ones do!