If you can serve 1K users with 10 employees, you can probably serve 1M users with 10k employees.
To add something useful as well besides snark, first of all, there are hard physical limits, which are sometimes well within context (you really shouldn’t try to outcompete light speed for example, relevant in some high-freq trading, infrastructure projects). Then you can try to increase headcount to any number, you won’t produce for example a better compiler. There are simply jobs that are more “serial” - the only way to win at those is to try to employ the very best of the field in a small team.
“Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.“ -Andrew Tannenbaum
1M users and 10k employees is not in the range where you have crushingly impactful logistics.
Each employee adds some overhead, which requires more employees... which requires more employees.