You're confusing potential with reality, and missing a basic fact of economics -- making something more expensive discourages people from buying it, making it cheaper encourages people to buy it. What matters is revenue (which is number of units sold times price), and profit (revenue minus costs) is derived from that.
If you sell 50 oranges at $1, by dropping the price to $.90 you are hoping to sell more oranges to make up the lost profit. What if $.90 is the sweet spot and now you sell 100 oranges.
To use your logic, sell one orange at $50. Then you do 1/10th the work and make 4900% profit. Now the problem is, who the heck is going to buy an orange for $50? Nobody. You will go out of business. So there is a bell curve science to it. Set your price too high, and nobody will buy. Set your price too low and you could sell lots of units, but make little profit on each. The key is to find the sweet spot, where you still make some profit but sell enough units that it's worth it. Apple has traditionally been in the high end of the bell curve -- expensive with small market share.
Something badly missing from your example is how much your wholesale costs are for those oranges. Let's say it is $.75. Sell 50 oranges at $1 each and your revenue is $50, your costs $37.50, thus your profit is $12.50. Drop the price to $.90 and say that's the magic point where people buy tons of them and you sell 100 oranges, your revenue is $90, your costs $75, thus your profit is $15. You're now making more money by selling your product at a cheaper price. Very simple.