Because that's not how games work - they don't run "at minimum capabilities" and they run their game loop constantly, rendering graphics. This means that it will almost certanly saturate at least M1s GPU and probably at least one of P cores. At that stage, even the M1 starts drawing a lot of power which needs disspiation.
Also Civ 6s target GPU is much faster than any of the M1s (which, despite the marketing, are still mobile CPU/GPU SoCs, not high clocked 100W+ TDP desktop CPUs with a separate 100W+ TDP GPU) so you won't see it use less than maximum what GPU (and CPU) can handle.
Don't mix performance profiles of games with performance profiles of bursty desktop browser software running Electron.
Also Civ 6s target GPU is much faster than any of the M1s (which, despite the marketing, are still mobile CPU/GPU SoCs, not high clocked 100W+ TDP desktop CPUs with a separate 100W+ TDP GPU) so you won't see it use less than maximum what GPU (and CPU) can handle.
Don't mix performance profiles of games with performance profiles of bursty desktop browser software running Electron.