Educate me. (Gently, please

)
I had to figure out BYB meant "back yard breeder." I knew what a puppy mill was and my Jorja didn't come from a pet store.
I am a new to the world of pets. I have never liked dogs or cats at all and only until recently, say since August, have I even held and cuddled a dog. I know. I know. Whatever you're thinking, I know.
Here is what I don't understand. And, like I said, please be gentle.
What is wrong with back yard breeders? The general tone I get from reading YT is that anyone who breeds dogs for profit is heinous. Why?
My daughter has a male and he is responsible for my falling in love with Yorkies. I puppy sit him while she is in college and he has been a delight. I read somewhere that Yorkies are like Lay's potato chips...you can't stop at just one. I knew there would be a day soon that Jett (daughter's Yorkie) would not be with me daily.

He has been so good for my clinical depression and anxiety! He makes me laugh and just having him sit on my lap and stroking his coat is therapy. I began my search for my own companion. Long story short, I received Jorja as a gift from my husband and children just two weeks ago.
Jorja is so precious. She and Jett are best buds and they rumble and tumble and tag and play all day long. At some point I know they are going to find another activity and we will do doubt have Yorkie puppies. Will I keep them? Not all of them...but I can see myself having two or three Yorkies scampering about. I know my cousin would like to have a Yorkie and I am sure I could find homes within my extended family for a couple more.
So anyway, I'm guessing this would make me a BYB of Yorkies if I allow Jorja to have a littler or two. Why is this a bad thing?
Again, please be gentle. I have a tender heart and truly just want to be educated about this.
TIA for your thoughts, experiences, and patience.
~Michelle (human to Jorja)