Why would a train going further be expected to have a lower average speed? Isn't it normal for trains that go further to run if anything faster? 170km/h is a fa

Why would a train going further be expected to have a lower average speed? Isn't it normal for trains that go further to run if anything faster? 170km/h is a fairly normal average speed for a long-distance train in Europe running within a single country, which is what they were comparing to.