It's like the person in a long ice cream line who needs to ask for a dozen samples one after the other, but this then makes the ice cream store stop giving samples entirely.
If the ice cream store was selling ice cream on a 70% margin, they wouldn't give a crap about how many licks of a tasting stick that customer would take, as long as they bought a scoop at the end of the day.
Clothing retailers don't, either. They make way more money from someone who buys 50 dresses a year and returns 45 of them, than from you agonizing over a single shirt purchase.
* Doesn't hold up line.
* Retailers encourage/enjoy behaviour because it means more sales as people aren't worried to return stuff they don't like.