Why block space is scarce
Bitcoin blocks are produced roughly every 10 minutes and contain a fixed maximum of roughly 1-4 MB of data (depending on transaction type and SegWit adoption). This is a deliberate design choice: a smaller block size keeps the blockchain easier to verify and validate by low-spec nodes, maintaining decentralization. However, it also caps throughput to about 3-7 transactions per second, far below payment networks like Visa.
When demand for transactions exceeds block capacity, a queue forms (the mempool). Miners prioritize high-fee transactions because they get to choose the most profitable transactions to include in their next block. This creates an auction: if you want your transaction confirmed in the next block, you must outbid others in that queue by paying a higher fee.
Fee dynamics and protocol limits
During periods of high demand (bull markets, NFT frenzies), fees spike dramatically because many users are competing for the same scarce block space. During quiet periods, fees are minimal because capacity is underutilized. The fee market is a self-regulating system: high fees incentivize users to batch transactions or move to alternative chains and layer-2s, which reduces mempool pressure and eventually brings fees back down. This is an explicit trade-off: Bitcoin prioritizes security and decentralization over throughput, accepting slower and costlier transactions as a necessary consequence.