Proof of work networks produce blocks at a roughly constant rate even as the computing power devoted to them changes enormously. A feedback mechanism enforces that pace.
Mining is a search for a qualifying hash
Miners repeatedly hash candidate blocks with varying inputs, looking for an output that falls below a target value set by the protocol.
There is no shortcut. The only method is to try, which is why the process consumes electricity in proportion to the number of attempts made.
A lower target means fewer qualifying outputs exist, so more attempts are required on average before any miner finds one.
Retargeting compares actual to intended timing
At fixed intervals the network compares how long the preceding stretch of blocks actually took against how long the protocol intended it to take.
If blocks arrived faster than intended, difficulty increases. If they arrived slower, difficulty decreases, and the adjustment is calculated from the observed timing.
Every node performs this calculation independently from the same chain data, so no coordination or governance decision is involved in the change.
The result is a self correcting pace
When more machines join, blocks initially come faster, and the next adjustment raises difficulty until the interval returns to its intended average.
When machines leave, blocks slow, and the following adjustment lowers difficulty. The network converges back toward its target without any central operator.
Between adjustments the pace can drift noticeably, which is why block times observed over short windows differ from the long run average.
Miner economics respond to the same variables
A miner's share of rewards depends on its share of total network hash power, so rising difficulty reduces the output of unchanged hardware.
Costs are dominated by electricity and equipment, which is why mining concentrates where power is cheap and why operations relocate when conditions change.
These are descriptions of how the incentive structure works, not assessments of whether any mining activity is worthwhile for a particular participant.
Security is measured in cost to attack
Rewriting recent history requires redoing the accumulated work, so a higher total hash rate raises the expense of attempting to reorganize the chain.
Difficulty is therefore a rough indicator of how much real world cost stands behind confirmations, which is why exchanges wait for multiple blocks.
Proof of stake networks reach a similar goal by a different route, substituting economic penalties on staked assets for the energy expenditure entirely.