Imagine you sell widgets for $200 a pop. Widgets are hard to manufacture, production is limited. Someone else has 10k widgets that they want to sell for $75 per.
If you buy all the stock, people will be forced to buy yours, because of supply constraint.
200-75 = 125 is more income than if you price-matched and sold at 75.
Now why destroy them, and not just sell them back? Well, they're not necessarily identical to the widgets you make. Maybe they have the other brand's logo stamped on them. Maybe the datasheet doesn't quite match.
Either way, your customers might notice. If you just buy and burn, no one downstream of you sees anything, except for higher prices
Note also that the above sounds immoral enough to be illegal in a whole lot of countries, so I would advise you not do that, though I'm neither lawyer nor spiritual advisor.