I'm pretty sure this is market forces. Glut of savings --> low rates. Sure there are local exceptions and regulatory impacts, but those generally can't stand against the tide, so I'd say it's 95% natural.
> inflation of money supply
Depends on the currency, but in the case of USD, increasing the supply is necessary to avoid deflation, which would seem superficially good for savers, but would be disastrous for economic productivity.
> high taxes on earned income
???
> subsidies to speculators (housing subsidies)
I don't know much about this one, but I think most subsidies are homestead-y (to owner-occupiers and first-time buyers).