The reason I gave in the post: if it were not the case, you could not bid a high enough wage to both a) make a profit and b) produce a discretionary income attractive to engineers.
If you want a further explanation of why that is, then I would say that it's the proximity to related talent and investors adapted to this kind of work.
Edit: In case it wasn't just a clever attempt at synecdoche: it can't be proximity to the Golden Gate bridge per se that increases productivity, because the North Beach/Marina/Marin tech jobs pay less than SoMa and SV tech jobs.
If you want a further explanation of why that is, then I would say that it's the proximity to related talent and investors adapted to this kind of work.
Edit: In case it wasn't just a clever attempt at synecdoche: it can't be proximity to the Golden Gate bridge per se that increases productivity, because the North Beach/Marina/Marin tech jobs pay less than SoMa and SV tech jobs.