There are a few factors which can make prices go down:
- The flight is not filling up as fast as they expected. Usually they have pre-defined prices for a given flight which increase as the flight fills up and/or as the date approaches (because people who want to travel at short notice are often willing to pay more), but if they have a hard time filling all seats they can reduce prices.
- Promotions and sales. Some airlines have regular sales for marketing reasons during which they will drop prices or increase the number of seats sold at the lower prices.
- Large numbers of cancellations (or more often, date changes since many tickets can be changed but not refunded). This is usually related to external factors like geopolitical events
- Addition of capacity on a route.
- Changes in fuel surcharges related to fluctuations in fuel prices and whatever contracts they have in place on this subject
- “Correction” of previous increases. For instance Covid disrupted travel a lot and on some routes whatever few flights were left were sold at a premium. Once the crisis is over, things get back to normal.
Like you wouldn’t expect to be charged more if the price increases after you booked, you can’t expect to get a refund if the price decreases. It’s exactly the same as if you bought shares in a company or bitcoin or gold or gas at price X on a given date, if the price goes up or down after that, you can’t say you’ve been deceived. That was the price on that day and that’s about it.
If your ticket is flexible you can try to rebook (taking into account any penalties).