You have to understand how airlines sell seats and make money. All airlines have sophisticated revenue mgmt systems and they sell seats pretty much the same way.
In a nutshell, if they have 54 seats in economy class, they sell them for different prices. For example, they will split 9 seats into different fare buckets - each fare bucket sells for a different price and have different fare rules. As the cheapest fare bucket sells out, the prices move up because the next bucket is priced higher. And so on.

Prices can also fluctuate, intra-day even. This depends on revenue mgmt projections and takes into account competition, demand/supply etc.

In the end, by doing this, airlines can break-even/make a profit even if the plane is not full. If they did lower the prices at the last minute, they there would be an unhealthy expectation to do so by their customers. By not protecting their price, they create last-minute demand and they cannot expect a premium for their higher buckets.

Like I said earlier, all airlines do this. Not everybody pays the same price. That guy that buys that last-minute ticket is effectively subsidizing other passengers.

Finally, airlines need not even sell that many passenger tickets in economy because these 2 categories sometimes cover the whole cost by themselves
a) cargo
b) premium passengers i.e. business and first class - the margins are much much bigger.

To maximize their revenue, no major airline will discount their seats at the last minute. Budget airlines may be another story - their inventory control seems much simpler and they don't list fare buckets (not that I know of).

Airlines would rather seats go empty than sell at a discount. Pricing theory is a complicated science but think about this - luxe brands like Hermes/Chanel do not discount because it weakens the brand. They will destroy old stock instead of farming them out to a discounter/outlet.

Same for airlines - consumers, usually business flyers, very often purchase last minute tickets. These folks get hit, airlines get better margins, and that's the nature of the business.

Like I said before, discounting at the last minute is a slippery slope - it brings about the market expectation that they will will always try to sell a seat. Nobody would then buy a ticket except at the last minute. Additionally, last minute sales at little margin is a lousy business. Businesses stay in business because of advanced cash flow and also having visibility in their sales funnel. Ask any direct sales force, last minute sales will get you fired.

As to airline alliances/partners - agreements do NOT cover pricing. These airlines partner with other to cross-sell their products (codeshares) or for route efficiencies e.g. I can sell more if I can "seamlessly" connect my network to your network - value. Airlines CANNOT collude with each other on pricing - this is against the law - wasn't it MH that go recently fined big time (or was it SQ?) by the US authorities for colluding with others on cargo pricing?