That's because most people use cash money primarily as a currency (trading token) and measure, not as a savings vehicle. As long as the value of the money stays relatively stable over the course of a couple of months, it works fine as a currency. You just have to spend it within those months. Most people and businesses scrape by, from month to month, so they just don't really give a shit about inflation unless it goes above 50% per annum or so.