But is inflation needed?
It is not necessary because it will cause problems for society and often inflation makes everything more complicated and in the end society bears the risk.
Why can't we just keep the currency at the same value?
The value of fiat currency will continue to devalue that's why we are advised to take it to a more productive place. Like trying to do business or invest because saving money will not provide added value for the future.
And why does it only happen to money? For example, the same wouldn't happen if we used gold as a currency instead. Is inflation a ploy that the government uses so people don't get rich off of savings?
Gold is different from fiat currency, the strength of gold can be seen when the economy is in trouble and gold can be stable to maintain its value. Directly the government also does not want inflation to occur because it can affect the stability of the country, but all policies that are implemented are sometimes not implemented properly.
If inflation is used as a tactic, then many countries will experience problems, unless a country tries to have an economic impact on other countries. They will try to suppress the currency of a particular country with existing policies and if a country's currency weakens then it will be quite risky.