Help me to understand why this is?

When the demand of gas/petrol goes up toward the summer the prices increase. (that makes sense) As more people fly, flight prices fluctuate. (some even charge extra for food)

But when fewer people are hand writing letters due to email, sending out checks in the mail to pay bills by banking on line, or sending out birthday/holiday cards using e-cards; Why does the price of stamps keep going up. Less people use stamps why make them more expensive?
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Profit maximization & demand elasticity.

Consider a restaurant:
Current price of a burger: $3
They sold 100 burgers each day for a year straight, at a profit of $2 per burger. Daily profit: $200

Then they notice for a month straight, they only sell 90 burgers. Daily profit: $180.

The owner does some research, and finds the following:
If she drops the price to $2/burger at a profit of $1/burger, they will sell 110/day. Daily profit: $110.

If she increases the price to $4/burger at a profit of $3/burger, they will only sell 70/day. Daily profit: $210.

Demand is decreasing because some people decide not to buy anymore at $3. But a loyal group of customers would buy even at $4. Even though demand is decreasing, the correct action is to raise rates (profit maximization).

One thing that many businesses struggle with is understanding how changes to their prices will impact the demand for their products (demand elasticity).

The USPS seems to have decided that, while fewer people are buying stamps, they are doing so for reasons other than price. Convenience, security, generational differences, etc. They figure that roughly the same number of people in the year ahead will buy stamps at $0.44 than would buy @ $0.43, so why not charge $0.44?

They'd likely charge more if they could, but they can only raise their prices a certain amount at a time (roughly speaking, with caveats: no more than the rate of inflation).
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The money from stamps helps to pay for the overhead expenses of the post office. The more money it can make on stamps, the less tax money it needs to pay for things like employees salaries, vehicle upkeep, and the cost of each actual post office. When everyone did their business by mail, personal and bills, the post office made lots of money from low cost stamps. Now that no one uses the mail, the post office is trying to stay in business by making the cost of the stamp met the cost of running the business. If they lowered the stamp back down, the people who don't use them now because of the internet probably still wouldn't switch back, so lowering the cost wouldn't bring back business. But raising the price for those people who don't do business on the internet will bring in some money. The government will end up closing even more branches of the post office. Some of the small towns where I live already have to get a PO Box because the town no longer has door to door delivery of the mail. Your pack of gum comment makes sense but a company like that can choose to go out of business or be creative about expanding business. What can the post office do? How can a business run by the government that no one wants to use but yet everyone sometimes needs stay in business? If a stamp only cost ten cents, would you put away your keyboard and get out a pen and paper and send a letter to a friend instead of an e-mail?
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Because the less people use them, the less money they make off stamps so they have to raise the price of them so they're not losing as much money as they would if they left the price the same.
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Like Jerry Seinfeild said about Tearing down his 20,000,000. $ house & putting another one in it's stead, "Because they can"........... Excellent question btw!! xxxxx