I think you're missing a critical part of how blockchains function: If Bitcoin was running on only 100 Mac Minis, there is nothing stopping someone buying 101 more Mac Minis, becoming dominant in the network and suddenly they can decide to just print their own bitcoins for themself.
The profitability of running Bitcoin miners is proportional to the market cap and the value of Bitcoin itself. For Bitcoin to remain stable, the total value must remain less than the cost of hardware to dominate the consensus algorithm.