why people do that ?
i am sure that model in market can cost more than 15 dolars.
no, i will not show the model.
i hate it when people doing that thing 
There are a lot of people with little to no development experience that complain about the price being high, even when it is perfectly appropriate for the quality of the asset. So, you end up pricing the asset low to avoid these complaints, and have to hope that enough people buy to keep working here profitable.
It’s the never ending race to the bottom. People are bringing their cheap Unity assets over from the asset store that were made with minimal effort and ported with even less effort and then spends the majority of their time taking very nice screenshots with flattering lighting and from just the right distance and angle not to show just how poorly made an asset is. Your inexperienced developer see’s two packs of the same thing, one which is $9.99 and the other which is $49.99 and of course buys the cheaper one because they want to save the $40 and hey the screenshots look pretty nice. So the experienced developer has to drop the price just to compete at all or deal with the fact that 7 times out of 10 they’ll loose the sale to that cheaper asset