Because doing this inflates the price of everything, including the exchange rate.

Imagine the following (simplified) situation:

Before inflation, a beer costs 10CHF, Euro is at parity: 10EUR = 10CHF = 1 beer

After inflation of 10x, beer now costs 100CHF: 10EUR = 100CHF = 1 beer

In the end, if you pay in EUR, a beer always costs 10EUR. The value of the CHF has not really weaken (only numerically)