The difficulty adjustment does fall, it just falls much slower when the price drops than it rises when the price increases. The reason why has to do with the economics of mining operations.

Mining has several costs that need to be considered, the first is the initial cost of the time and money to set everything up. This would be contracts for energy and the purchase, relocation, and setup of the equipment to begin mining that energy into Bitcoin.

The next cost would be the upkeep, staffing, rent, maintenance, and energy costs.

When the price is rising it's easier to invest the primary starting cost to get the operation running and/or expanded, once setup the continuing costs of keeping the whole thing going is much lower, so they can keep mining even at a temporary overall loss considering their original investment, as long as they're still marginally profitable given the operation is already in place.

When the price is falling, the only cost that matters is the marginal continued maintenance and energy costs. The initial investment has been made, it makes little sense to completely shut down an operation during a temporary dip if they're able to keep running at marginal profit. Marginal profit is better than zero profit.

These factors mean mining operations reacts to upside price volatility much more than it reacts to the downside and, since the market reverses quickly, it causes resistance to the downside and helps increase confidence in the network which increases the value and raises the price again.

Take a look at the last 1 - 3 years (attached) and compare the price action to the difficulty adjustments. We're still in a bull market, it's just difficult (heh) to see when focused on the price.