The Chinese government has been saying that Taiwan belongs to China and amassed navies every year for almost 80 years now. (Longer if you count previous governments.) Base rates are important because what you think is a highly significant trigger event that will surely have major consequences may actually be a frequent occurrence that is typically inconsequential.

Or in other words, if you want to say "this time is different" and deviate from the base rate, you actually need to look at the previous times to find out whether it really is different this time, and if so, by how much.